I was doing the Hodir spear throwing daily (the one where you ride a dragon and try to kill it via prying its jaws open and using the spear) on my DK, died, and went into ghoul form while still in the dragon. I couldn't do anything except wait to die.

When I resurrected and tried again, some of the hot keys did not work, so I had to just wait to die (the one I recall distinctly was the "4" key, which is the major strike).

Reloading UI didn't work, I worked around this by exiting the game entirely.

This is a known issue with vehicles and pets.

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Maaven
Blizzard QA