The ability failure bug for melee classes, I've found, ALWAYS happens after using any off-the-gcd ability, like retaliation. After using it, my next 1-3 abilities "fail". Vicious slash, for example -- my character will wind up her lightsaber, but then stop.
I'm not, I guess, super far in the game, but so far, my choice of Vengeance as a tree seems to be severely inhibited by the fact that I cannot burn my excess rage with retaliation without rendering myself unable to attack for the next few gcd's.