Patch number 3 for Beta 13, you can read about what was patched yesterday here and the reasoning behind some of the changes here.

Patch notes:

• Fixed issue where swapping weapons would sometimes swap the wrong weapon
  
• Fixed issue where sometimes when swapping weapon to slot that had 2 one-handed weapons, one of them would get destroyed.
  
• Fixed issue where dragging items into slots where items already existed would destroy those items.
  
• Fixed issue where the grenade slots would not have any tooltips.
  

Please make sure to restart steam completely and verify the integrity of the game files!