I was using the Salvation of Bakka - Beta (grey skin, default mag) with the skin of Drogos Reclamation - Alpha (black skin, drum mag). However, after an indeterminate number of reloads, the bigger drum was spawning in the offset position of the smaller magazine, and was overlaid with the actual model of that other magazine, as seen by the protruding skull
KSIVA available on demand, but I suspect it won't be necessary