Hello, I'm really glad you liked it. :)
To stash the loot, you need to press the key for environmental interaction ([Enter] by default), then choose the "go back" option – then, your backpack should be emptied. If that's not the case, then it surely is a bug, and it would be a great help for me if you would send me the save file (basically every '.gob' file from the game directory).
Could you please tell me what version are you playing? Windows / Linux, Tiles / Text?
edit: I can replicate the bug locally too, it's hard to believe I didn't test this functionality! Thank you for your report, I'll publish the hotfix even today.