PC Board Damage

[nre]

The last McIntosh amp I worked on showed this issue on the preamplifier PC board.  The traces are wrinkled and blistered.  I've seen this before on other first-generation solid-state amplifiers.  I presumed it was thermal distress from a de-soldering heat gun but was unable to replicate it using another board.  I'm thinking it's a Quality problem with the board.  This particular board came from an MC2505. 

It works fine, the traces are still conducting but I've replaced it regardless with a new board.