Haven't received mine yet from GP. Now that I am aware of this problem, I believe the glue has not had time to completely cure. Heat on uncured glue will cause it to soften. I'm sure most everyone with this problem had their tablet on for an extended time, maybe even had it plugged in at the same time.
When I get mine, if doesn't have this problem, I intend to only use until it gets a little warm then turn it off and let it cool. A few cycles of this for a day or two should cure the glue so it will never soften from heat again. Just a thought, could be wrong.