I used this tissue when it was first released by Lion Picture framing (and Hot Press) sometime in the late 1980's, I'd previously used Ademco tissue. It's a temperature/time issue causing shrinkage, I found the tissue had a lower melting temperature & required less time than the Ademco stuff I was used to. Tissues changed because people were mounting RC prints where too high a temperature damaged prints.

My Ademco press only has high & low settings and is either full weight or nothing but I still used the high setting but cut the time substantially, that was enough to get a good bond (still all OK 20+ years later) but not transfering all the heat through the top/bottom cover boards.

I think if that tissue gets too hot it gets into the board and shrinks it pulling from the edges (capillary action) I did get the same when I first tested it. Hot Press make their own presses which use glass so don't get as hot as my Ademco with it's cast iron parts.