While using Dual Pistols on my Sentinel and my Blaster, it will sometimes revert the skins to the very first entry on the weapons skin lists (Semi-Auto), while keeping the colouring.
I'm not sure what exactly triggers them to change, though I suspect that it's changing costumes though I can't reproduce it consistently.
I use the pistol skins Celestial Pistol on one character, and the Plan 9 Striker and Quartermass Pistol on the second character.