This only started with the release of 3.3. I'm guessing it has to do with the reported backend changes to oGCDs, but who knows.

Example of what's happening:
Cure on 1
Cleric Stance on Ctrl+1
Using Cleric Stance will also simultaneously cast Cure.

It is not limited to this pair of abilities, but seems to only occur with oGCDs with very short animation locks. Convalescence and Presence of Mind are other examples. It also does not happen every time, but it is frequent enough to cause problems. It's MUCH more prevalent in instances, occurring 1/2 - 3/4 of the time. While outside of an instance it can still be reproduced but significantly less reliably. I've lost numerous GCDs while raiding, and it's growing incredibly frustrating.

Please, for the love of dog someone help me out with this.