This is curious. I've fired thousands rounds lead in several Glock pistols and never seen this. Maybe a better lube is in order? I dunno. If lube got into the inerds, I can see this happening in really cold temps. It's possible the lube vapor condensed on the cold metal. Paraffin and bees wax will do this. If the case wasn't sealing the chamber, you'd see other signs of it. Eventually, you'd have ejection and/or chambering issues, even with an OEM barrel.
What load was this? (bullet, powder, charge, lube)
Life is tough. It's tougher if you're stupid. -- The Duke