"Floor one is where I sell Arcane tomes. Magic studying is SO much more awesome than the normal kind! You can learn new skills using them." says the witch.
I'm assuming you're talking about the boss at the end of the snake clan cave? If so the treasure in the last room is decorative, you can't take it because it's stolen from other people. The characters should've suggested you go back to Oasis to report it, after which you'll get a reward. I'll consider making this clearer in future versions.
I found the bug and reproduced it, then tested a fix which resolved the issue. All platforms of the game have been upgraded to version 0.9.1 with this new fix in place. You should be able to download the appropriate files then simply move your saves into the new folder and continue playing. If that doesn't resolve the issue let me know. And thank you for finding this bug!