Hi Sergio,
I am not seeing this happening in our latest main stream. So it seems it may have been fixed at some point since 5.4. We have had some reports around it, but never were able to reproduce this internally. A few thread safety improvements were added (CL 38336184), and we added some more/better MT access detectors (CL 38249957). Both of those changes will be in 5.6.
-James