After reading this thread, I found out I had the same issue with my X as well. Not so often, around 3~4 out of 10 times, usually happens when the car is cold and after a short acceleration.

This issue is TOTALLY GONE after I did the transmission fluid change using Royal Purple. I haven't tried other brands, and this is my 1st time transmission fluid change. So overall it works pretty good on my X now. Just a little bit worry about whether the fluid pumped in is enough.