I'm curious has the game been fixed, where the gallery will clear itself out after saving and closing the game down?
For which gallery?
And are you sure your antivirus isn't keeping the game engine from writing to the save?
The engine is writing persistent variables, which means as soon as you see or obtain a gallery CG it should never leave.
It shouldn't be possible that they aren't being saved, unless something's keeping Renpy from writing a file named "persistent" into the save folder.