I use the CB1100 wad (7625 powder) and haven't had any cold weather problems. I shoot all winter long and it's down in the single digits sometimes.
What I have found is that trying to get a couple of extra reloads out of a case will let you down with a blooper now and then during the cold weather.
I'm guessing the weak crimp from over use just isn't allowing complete combustion,,again just a guess.
Seems as though you can get away with some so-so condition cases like that with a powder like Clays, but not so with 7625 (in cold weather).
A good reason to toss some of the hulls and start using the inventory stored in the garage I guess.