Hello, I don't know if this is a known bug or something only happening to me but when i accept the quest in Moonglade 'Trial of the Lake', the timed one, my screen freezes and i can't do anything, i have to close WoW and when i try logging in it comes back into a frozen state.
After a while it fixes itself but this is very frustrating!
Hey, I've recently done that quest on Medivh and didn't have any issues. It sounds like a graphics or addon error, possibly with your timers. Maybe try disabling your questing addon to see if that helps.