Rammus Taunt not Working Right

I've been experiencing a problem with Rammus' taunt. I'll click an enemy, and when Rammus gets to the enemy he just stands there and never casts the taunt. Not every time, but enough to take notice. I also notice sometimes an enemy will just stand there for the duration of the taunt without attacking Rammus. This happens after the enemy casts certain abilities like short dashes. It's been happening for a while now. Anyone else experiencing this issue?