It appears that the problems with the navigation system occur in more than just the Explorer and at least in model years 2011,2012, and 2013. This is clearly a design flaw in this system though I'm sure that Ford would be unwilling to acknowledge this.
Just took my 2011 Explorer in for another attempt at fixing the problm. Dealer located TSB 12-11-2 and reprogrammed the GPSM to the latest level. Dealer said that if this didn't fix the problem I would need a new module. On way home the nav performed perfectly & I thought my problems were over. However, next day system was worse than before, sometimes locking the cursor on the map screen totally. Ended up by disconnecting the negative battery terminal for about 5 minutes, which temporarily got the system working again. (The TSB 12-11-2 at the dealers involved disconnecting the battery) Seems to me that what this does is to re-boot the computer in the nav/MFT system. If the fuse box were more sensibly located, it would be far easier to simply pull fuse 29 (on my Explorer) to temporarily power down the nav system, but this is another piece of bad design.
Suggest using the 'Delayed Reboot App'
http://outofmytouch.com/reboot.html which is much easier to use and appears to work as well as disconnecting the battery.
Clearly the Ford software needs to be re-written.