Hi!
I ecountered the same problem I always had with IrfanView used portable before it came out in PAc-format. I just didn't remember the issue before.
When switching through options to change to preferred settings, irfanview portable hijacks file associations for images if I don't remeber to uncheck that. I was confused when all my settings from my local installation were gone, but then realized that Irfanview was started from my still connected USB-drive (bypassing its launcher as well ).
When I unplugged it, all associations were gone. I had to start IrfanView manually and check options, then all was fine again as IrfanView restored its associations from its local settings file.
It's not a real problem when you know what to do, but I consider it a design flaw. Maybe it is possible to backup the local settings first and then switch back after the PA.c Version quits.
dj
-edit-
Unchecking is no remedy. And associations are not gone but unfunctional after unplugging. (See post below).
As long as I don't change settings, all is fine, but that cripples IrfanView a bit as e.g. Fullscreen options are done with the same dialog-box.