Yuumi's passive seems bugged as it doesn't restore mana. It happened to me on EUW yesterday in a custom game.
But i am sure it happened to me before in normal games.
_**Welcome to Bug Reports!**_
Is there something you really can't do without in the client? Is Udyr displaying as a Picasso painting again? This is the place to report bugs in League of Legends!
Follow the **[Universal Rules](http://boards.euw.leagueoflegends.com/en/c/announcements-en/3eWpXbJi)** and keep content focused on appropriate topics for these Boards.
Use the report button for any post you think deserves the attention of our moderators.