Groove~ with timestretch not synced to global transport in a poly

Hello all,

I am having this problem. I work with timestretched grooves~ in 12 different polys. I dynamically switch the timestretch on or off. Sometimes when I play the timestretched loop, it doesn't play synced to the global transport. I think this comes from the fact that I start the loop and tell it to timestretch at the same time. I guess timestretching takes some time, say 30 ms, and then the loops starts playing (off course, with this 30 ms delay). The weird thing is that it only happens sometimes (sigh)...

Lock is on, followglobal tempo is on and I use the efficient mode, quality good. It happens with all the modes or qualitys.

How could I solve this? Playing a loop on time, and telling it to play it stretched at the same time.

Cheers