I was playing a PvP and I cast Whimsy on a Heimerdinger on the enemy team just as I died.
I didn't realize until a couple minutes later that Heimerdinger was stuck in squirrel form for the rest of the game, but could still cast spells and attack normally as far as I could tell.
Sounds like the problem was only on your end; your client never changed his character's texture/model. This is still a bug though.
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