It's not a bug, it's a quirk of the aggro system. That means it's not going to be changed unless the game's aggro system is rebuilt. I'll try to explain exactly how it works.
Enemies have a list that they use to keep track of how ticked off they are at specific players. Whenever someone uses a power on an enemy, they get put on this list if they aren't already on it, and if the power does damage there's a big equation based on archetype and amount of damage that decides just how ticked off the mob is at that person. Even if a power does no damage (flash arrow) using it will still put you on this list and give you a small amount of threat.
Imagine an eight man team. Person A uses flash arrow on the enemies. At this point, the enemies have Person A on their aggro list, but they haven't been alerted so nothing happens. Person B is a scrapper with no taunt aura who runs into the group. At this point, the enemies have been aggroed and will begin choosing targets. There is only one person at this point who has used a power on the enemies, and that is Person A. Now, enemy groups make an effort to split up their attack among multiple people, so it's not like every fight you use flash arrow all the enemies will immediately spank you, and you probably won't even notice this phenomenon if you're teamed with a tanker that opens every fight with a big area attack, but over time it is very likely that you will notice that you are on the receiving end of a large portion of the initial enemy assault.
I hope that explains the weird aggro thing. I'll move on to the power itself. Flash arrow is actually a pretty weak debuff. It's 9.75% enhanced (6.25 base). Against even level enemies, this is exactly the same as buffing your entire team for 9.75% defense, except even better because you don't have to worry about exotic attack types like psychic. This seems like a decent deal, but compare it to the debuffs found in other sets. Dark miasma has two debuffs (darkest night and fearsome stare) which BOTH debuff by about 29% when enhanced, radiation infection is about 49%, and storm summoning has hurricane which hits for 58%, though it's not easy to use.
The only advantage flash arrow has over these much more powerful effects is that it is tagged to be unresistable, meaning that an AV's ability to resist most debuffs by about 85% does nothing. Flash arrow is already 1/5 as strong as other debuffs though, so this isn't that big of an advantage. Against an even level AV, flash arrow will be 9.75% and hurricane will be about 8.8%. In other words, flash arrow is 30-40 points weaker than other to-hit debuffs against most enemies, but against AVs it has a 1% advantage.
Thank you very much. I think I understand. Basically, it sounds like the weird aggro only will happen if I use Flash Arrow before we aggro the spawn. If I use it after the fight begins, it's just like any other debuff. Is that correct?
As for its efficacy, yes, it's not amazing, but one of the things I like about TA is that it seems to have so many different smaller debuffs.
Wrath smash good.
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The -Perception debuff is nice too. I'm also a fan of pointing out the mechanism of the debuff. A targeted large AoE autohit power with a decent duration. Powers are more then just the raw numbers.|
Originally Posted by Garent
The only advantage flash arrow has over these much more powerful effects is that it is tagged to be unresistable, meaning that an AV's ability to resist most debuffs by about 85% does nothing. Flash arrow is already 1/5 as strong as other debuffs though, so this isn't that big of an advantage. Against an even level AV, flash arrow will be 9.75% and hurricane will be about 8.8%. In other words, flash arrow is 30-40 points weaker than other to-hit debuffs against most enemies, but against AVs it has a 1% advantage.
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Edit : Deleted first sentence. I thought I had seen it asserted somewhere that the -Accuracy debuff wasn't affected by level but can't find any references stating that.
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Yup, that's right.
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Originally Posted by Ebon_Wrath
Thank you very much. I think I understand. Basically, it sounds like the weird aggro only will happen if I use Flash Arrow before we aggro the spawn. If I use it after the fight begins, it's just like any other debuff. Is that correct?
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I was just wondering.... do the effects of FA stack? Looking at Mids the duration of the power is 60s however if you perma-hasten you can get the recharge down to approximately 5 seconds. If the effect stacks then 5 applications will apply just under 50% debuff wont it - which would be invaluable against an AV - especially if the AV just sits their picking his nose while you fire it off!|
Originally Posted by Garent
The only advantage flash arrow has over these much more powerful effects is that it is tagged to be unresistable, meaning that an AV's ability to resist most debuffs by about 85% does nothing. Flash arrow is already 1/5 as strong as other debuffs though, so this isn't that big of an advantage. Against an even level AV, flash arrow will be 9.75% and hurricane will be about 8.8%. In other words, flash arrow is 30-40 points weaker than other to-hit debuffs against most enemies, but against AVs it has a 1% advantage.
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I'm not sure how stacking or the maths works so I may be completely wrong but thought I would ask the question.
Life is one big practical joke that we as the human race have yet to see the punchline to. Once you work that out the rest is easy.
As with most debuffs, you can't stack from the same caster.
However, it will stack with other peeps FA which could add up to a significant difference.
You basically have a auto-hit non-aggro 60s debuff with significant -perception (good when two groups are close together).
The other more powerfull debuffs mentioned are all toggles with pretty decent end costs.
Tactics:
If you are going to use flash arrow in a group, break line of sight before the group gets aggro'd. Mobs that don't get aggro'd by the tank/scrapper/other that starts the fight will move to be able to see you and run smack into the rest of the group for a proper thrashing. 
I thought I remembered something about Flash Arrow's debuff being non-resistable. Have I been eating the lead paint again?
And does that mean it's the same -9.75% against +3s? Archvillains? Hamidon?
Mini-guides: Force Field Defenders, Blasters, Market Self-Defense, Frankenslotting.
So you think you're a hero, huh.
@Boltcutter in game.
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/nitpick|
Originally Posted by Darklight
As with most debuffs, you can't stack from the same caster
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Generally speaking, everything stacks.
But yes, flash arrow does not stack from the same person.
Fulmens: Yes, it's unresistable. I mentioned it in the last paragraph of my tldr inducing dissertation. I'm not absolutely sure of this, but I'm 95% sure that level modifiers will still affect it. Unresistable just means that it will ignore to-hit debuff resistance that AVs have.
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True, the debuff can't be resisted, not even by AV Resistance.|
Originally Posted by Fulmens
I thought I remembered something about Flash Arrow's debuff being non-resistable.
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HOWEVER... go to the last paragraph for more.
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| Have I been eating the lead paint again? |
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| And does that mean it's the same -9.75% against +3s? Archvillains? Hamidon? |
The purple patch reduces all debuffs, damage, everything that affects enemies. It's not resistance, it's an outright reduction by XX% (varies by level of difference), so Flash Arrow is still subject to that restriction. +3 foes would experience only... 65% of the debuff, if I recall, resulting in a final debuff of 6.3375%.
I was reading up on Flash Arrow for my new TA/A defender, and there were a lot of different opinions about it.
I like the debuff. As a usual tanker (I have two 50's), I understand why it's powerful.
However, my concern is the aggro bug that some people seem to have found with it, saying that they immediately aggroed, even right from a tanker who had just taunted.
Is this bug still around? Is this arrow worth taking? I'm interested in gathering some opinions.
Wrath smash good.