Odd power firing with mouse targeting.

Was on a TF a few days back and noticed something odd...

Whenever I targeted with my mouse and fired my taunt, it would require 2 key presses. When I targeted with my tab, it would fire with one press. Note that I am not talking about whether the power hit... I am saying the power would not fire off.

I haven't actually tested with other powers, since I usually use the tab to target for most of them.
Anyone else have this happen? is it considered "normal"?