Ok, first things first, the bug:
If you log out while mounted, then log back in, your character will not be mounted back on their mount, but appear to walk normally. Then, if you try to swing your weapon, your character will start freaking out with animations, and it won't do any damage, and in the top left of the screen it will say that you are mounted.
For the suggestion: Add a blocker when using ultimates in between taps, or at least for cancelable ultimates such as werewolf transform. A couple times, I accidently double tapped my ultimate key, causing my character to start going into werewolf, then canceling the affect the second time I hit the key.