I've often noticed as I spam the mouse buttons, that the ability I am trying to activate doesn't seem to occur immediately, and instead may take a second or two while I finish other animations. Does this mean that I can create a short queue of abilities, or abilities always executed only one at a time? If abilities are queue-able, how deep can I queue them? I'd be happy to mash less if I knew my abilities were being queued. Queuing might also allow for short ability macros.
One ability will queue. If you activate an ability while another one is still active, it will execute after your current one is finished.
No more abilities will queue, however. This is what I concluded from quick tests. This is very important to the game, since it is fast paced and quick reactions are important. Queued-up abilities would hinder that immensely, since spamming buttons is an integral part of the game experience (at least... for me :P ).
Either way, queuing shouldn't have anything with what you're experiencing. What you're seeing can probably be attributed to two things: