O.o I've never gotten game freezing from going to the edges of the map on a Magic Shield Carpet (TM of Blacksmith of Little Blacksmith Shop)
I've been past the castle gate, under the castle, ontop of almost every mountain range I wanted and rode across the skybox (as in with my head generally pressed into the roof of the map until the shield was forced through my feet causing me to plummet back to the ground)
Perhaps the freezing part is more in line with a possible corruption in the data, (redownloading sometimes changes that) or more specifically with how you computer reacts to the information, and just doesn't like that information