Poppy ult cast bug

I am not entirely sure how to recreate this bug (unfortunately) but it already happened to me more than once (not entirely sure if two or three times total and in completely different games) and therefore it might be a recurring issue. The bug in question concerns poppy's ultimate cast. Usually if you start channeling your ult and don't use it after 4 seconds, Poppy stops her casting animation and the ult cooldown is immediately reset to 30. Nevertheless this bug cancels that. After the 4 second channeling, although Poppy's animation stops (like it would normally), and she begins walking around normally, the casting indicator of the ult remains (and at full range). After that if I press my left mouse button Poppy sends her ult at full cast power way after the 4 second max channeling, first time I think it was easily a 10 second interval between the beginning of the cast and the moment I used my ult.