When you hit a button for an ability, that ability queue's up. Any button presses after that are completely useless, unless timed to follow the first attack and queue up a second.

Seriously, you should never hit more buttons during combat then you use abilities. The queueing/activation system work fine. If nothing is set to go off, the stamina bar is the basic yellow/white. When something is queue'd, it turns blueish. Most of this is supported with chat log text.

I'm not trying to imply that 'you're doing it wrong' or anything, but 'something is' wrong if you resort to button mashing. Maybe you've got lag issues, either server or client side. Hard to say.