I can use Google maps and download offline maps by unchecking the Auto Connect in MSC in my Connectivity settings.
My phone is an Xperia Active and Google maps would only let me download maps if it had access to my SD Card, and when Auto Connect in MSC is checked the SD Card becomes inaccessible by my phone if I have it plugged in to my PC via USB.
Having it unchecked, the SD Card remains available to my phone whilst plugged in to my PC. So I can reverse tether and use my SD Card at the same time.
Using the "3G hack" with Google Play, I can also upgrade apps that are in my SD Card, that would otherwise not be read if my phone connected automatically in MSC.
Sorry if this info has been posted before.