Switch between gamemodes (creative, survival, and spectator) with a wizard staff in inventory (not hotbar) and eventually the item in the staff will vanish.

Hello Cinderheart!

Did this occur on a dedicated server? Because if so, this is unfortunately a vanilla/forge bug, and I can't do anything about it. See this issue for more information about it.

Yes sadly. Well, thanks for letting me know, now I know how to avoid triggering it.

Alright then, I'll go ahead and close the issue, since the bug is out of my hands.