optimized media crashing then unsyncing mono track

Upon trying to generate optimized media for a 4k clip, resolve crashes. Upon restart, all of my mono clips, which are formatted to ‘stereo’ in clip attributes, left and right source channel selected to ‘embedded channel 1’ are out of sync. The only way to “fix” them is to manually switch the format back to ‘mono’, hit “ok”, go back into clip attributes and change back to ‘stereo’ and ‘embedded channel 1’ for the right channel.

15.0.0B.057
Win 7 Professional