Hmm that can be it. This means be careful with Flash Arrow. Thanks for the tip Avalanche 
Can't really comment on Flash Arrow...Fleur Mortelle, my lvl 50 TA/A, has never used it. I took Entangling Arrow as my compulsory in TA and have never really regretted that.
One thing I will say though, is don't take both! There are so many powers you just have to have at higher levels - you don't want Flash and Entangling bunging up slots.
As for natural builds, Fleur is 100% natural, and proof that you can get all the way to Hero of the City with no travel power. She has Hurdle, 3-slotted with Jump SOs, and Sprint, 4-slotted with three Run SOs and one Jump. 3-slotted Hurdle is about the same speed as unenhanced Fly, and she can jump over the height of lampposts (blame it on extensive gym work and vitamins!) 
The 30 second jetpack device takes care of any awkward cliffs and walls, and she can even get around in Terra Volta with a bit of forward planning!
Good luck with your TA/A - I can truthfully say that levelling Fleur is the most fun I've had with any of my alts.
As I've had much experiecne with Trick Archery with my TA/A defender Longshot Lorrie I can say the following things about Trick Arrow:
1. It is a very nice debuff on top of our vast stock of 'em
2. It's to-hit list prioritising on us can easily by countered by using it in the middle of a fight
3. It's definitly a better choice than entangling arrow (Sorry Fleur XD)
And if you're interested in teh magical world of TA/A be sure to check out my guide for it at Lorrie's Guide to the Trick Archer
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As for natural builds, Fleur is 100% natural, and proof that you can get all the way to Hero of the City with no travel power. She has Hurdle, 3-slotted with Jump SOs, and Sprint, 4-slotted with three Run SOs and one Jump. 3-slotted Hurdle is about the same speed as unenhanced Fly, and she can jump over the height of lampposts (blame it on extensive gym work and vitamins!) The 30 second jetpack device takes care of any awkward cliffs and walls, and she can even get around in Terra Volta with a bit of forward planning!
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Lol, talking about "bunging up slots".
Fleur, you used 5 extra slots on hurdle/sprint and you got at least 1 or 2 more powers which need slots then when taking normal travel (which dont need extra slots really)...
Not even to mention that SS is only one power pick away from hasten.
And both flasharrow as well as entang arrow are very low on slots. Flasharrow doesn't have any need for any additional slots at all and entang arrow is good to go with just 2 accu (meaning one extra accu slot) or even just stick to the base slot with 1 accu.
Take both! 
Had you already flashed some of them once? There is a bug with flash arrow if you repeatedly flash mobs then the perception debuff drops between applications for a split second.
Try it out. Flash some mobs, move within aggro range and then flash again. They will aggro on you during the brief time that the debuff refreshes itself.
It's not so much a 'bug' though. It's part of the design that stops it from stacking with itself. It has to drop in order to refresh itself without stacking.