[Pyros]

This is not a bug, this is how it should be, because the game reads (each time a new campaign scenario starts) the variables/parameters of each core unit from the nation's OOB database.
So you can't customize CORE FORCE units.
You only may customize AUX units.

Concerning what you mentioned for the sniper unit (changing of the truck to a sniper unit), I tried to reproduce it but I couldn't achieve the same results (so I can't confirm your remark).

cheers,
Pyros