On my Tanker I often use back to back combos of Sweep and Attack Vitals and I have not noticed any bug there. Having said that though, those two combos don't share a power. I will try Empower and Weaker when I get home later and respond, provided someone doesn't beat me to it.
I still play for fun
From Liberty to Freedom
Any team level
A known issue.
I suggest waiting until completely finishing the animation, or fill the combos with brawl.
Your character does not have capped defense. Depending on your AT the cap is between 175% - 225%. Your defense is not teal in the combat window, it can go higher. STOP SAYING IT IS CAPPED! The correct term is Soft Cap.
I enjoy playing in Mids. I specialize in Melee Characters, other AT's usually bore me.
Yuck. Getting harder to like this set 
If it makes you feel better, you probably will only be using Blinding Feint-Attack Vitals for single target and Blinding Feint-Sweep for AoE at higher levels.
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So, I'm in game and have access to the weaken and empower combos so far. I successfully execute a combo, then immediately queue nimble slash to queue the other combo... and the orange circle around ablating strike, the next power, doesn't come up. This happens pretty routinely and is turning me off from the set...
What mechanic am I missing? Yes, I am hitting the target. Is there currently a bug sometimes preventing back to back combos?