On the reprap forum, Mark Rehorst posted:
I’ll be recementing the heater that is coming off the bed plate. I contacted Keenovo about it and they pointed me at a couple interesting links that say you should seal the edges of the heater with silicone after sticking it to the bed plate. Maybe that would prevent it from letting go of the bed as mine is doing.
The relevant link is this two-page PDF
Seal the heater edges with a thick bead of the RTV sealant.