Comb melted in hive

Seams a little quiet so I thought I would post.

When I checked the hives back in about Aug I noticed one of the combs had an area on it that looked like it had been melted (pic attached).  I have heard of bees using heat to kill an invader they couldn't fight off other ways.  Is that what I am seeing or is there a different explanation? 

In the same hive on the floor near the hive entrance under the frame with the melted portion was a large amount of propolis gluing the frames to the body and the floor.  Probably a blob equivalent to a spoon full of peanut butter.  I didn't think to cut it up at the time.  Entombed invader?