Think it happened with the update, but my PB changed from julius nifta to helix proi. As I went to use it I noticed the icon was different and sure enough out pops helix proi.
Anyway, only 8 excubes to change it back but I certainly find it odd that these things just spontaneously happen. It was a melee mag so I think it just reverted back to the default PB. The actions/triggers didn't reset though so at least I don't have to redo that stuff.