If you go to the north of the 3 vendors (crystal blom quartermaster) in the dragonfall pact command/outpost, and buy 5 mistborn motes right before reset (1 min before), then wait in front of the same vendor, it will cause the game to crash/hang. gw264.exe will hang and refuse to respond, and you can either close the program, or wait 10-20 sec for it to crash/respond.
After waiting, you are unable to buy the mistborn motes again after reset (and after talking to the vendor a second time), but the mistborn motes themselves will still be displayed in the vendor window, but with a max of 0. You need to then exit the map, and reenter, in order for the vendor to let you buy them again.
Edit: Also submitted a bug report with a screenshot attached.