Fireball shortcut key(F) sometimes refuses to work. I'm not sure what causes it, but once it fails to work once, it will not work again until you attack something or use an inventory item. Not sure if it happens with other glyphs.
Longstanding combat prediction(those tiny yellow marks at health bars) does not always work correctly. Two common issues I noticed include fighting monsters with death prediction(damage made by monsters to players after their death protection is broken is not displayed, also before breaking death protection combat prediction shows that the monster will have 0 hp, which is somewhat inconsistent with player death prediction) and attacking monsters that are lower level(sometimes combat prediction thinks that monster will attack first and therefore predict an additional hit for player, while player actually goes first).
While at it, it would be nice if longstanding combat prediction would predict your HP after death protection differently. It's currently impossible to easily tell whether you will be down to 1 hp because of death protection or just because the enemy attack dealt exactly that much damage until it's next hit that knocks you down to 1 hp, and there is quite a difference between the two situations.