Udyr Stun Not Working

i have found that using my E just before an auto attack mid animation maybe (changing forms from any other form usually my Q) will cause the person not to be stunned however the timer for when i can stun them is Activated meaning I'm unable to stun them even though i never did in the first place now i don't know if anyone else is finding this issue or not i don't see Udyr played much anymore but that's that....

1. Build up full passive stacks (might matter might not)
2. Change into tiger form (my issue specifically) or any other form
3. Mid auto animation or while attacking someone at the least change into Bear stance
4. Results?