What I have observed might confirm the 8GB limit. I have several USB drives with music on them, most of which are 8GB, but also have 16, 32 and 64 GB. I can confirm that the 8GB ones have no issues, but the larger ones, although they appear to work for the most part, have various problems which I have described in the new thread below.
http://www.mazdas247.com/forum/show...-After-Resume-Fix-(BT-Module-TSB-Replacement)
I am not certain, but evidence would indicate either there is a limit to the # of song files on a device, or a device size limit, or both that is causing the problems. If Mazda would just document the specifics then we could avoid some of these issues.