Chris Lewis wrote:

According to dpb :
The solvent problem I think can be discounted as being too far removed
in time and frankly the damage pattern just doesn't have the shape for
that to have been the cause unless it were a misdirected spray gun blast
and the reported application was rubbing w/ a rag instead...

While I'm by no means convinced of what the cause actually was,
the solvent was rubbed off with a rag.

I could see a solvent dissolving into the siding, and not showing
any physical effects until some time later when hit by high
temperatures because the vinyl's melt point has effectively
been reduced, and raises only slowly as the temperature forces
outgassing.

Eg: applied in the fall, doesn't show any severe effects until
full hot days in the summer, which have driven out the solvents
and the plastic rehardened.
--
Chris Lewis,

Age and Treachery will Triumph over Youth and Skill
It's not just anyone who gets a Starship Cruiser class named after them.

The OP indicated spring '06 for the solvent and it's now summer '07.
Summer '06 apparently went by with no issues.

Pete C.