My observation has been that the system doesn't seem to have a good GPS receiver. I have the trouble you are describing when there is heavy overcast or rain.

sometimes turning the system off and then back on will help. Its almost like if it doesn't get a good fix to start with... it can take it a LOOOONG time to figure out and correct itself...

I don't think there is anything "wrong" with it other than the fact that its just a poor GPS receiver... I wonder where the darn antena is for it. I woudln't think it used the radio antenna cause that is the wrong configuration for GPS signals entirely... but then again that would explain alot wouldn't it.

Anyway thats my opinion.... I don't seem to have the lockup problem others have described.