And yet again I had tons of fun watching you playing my game :)
Yes, the dungeon layout had changed since the original Knightin'. And it is designed in a way that makes to buy the last key to access the boss room. I can't leave a location until I collect everything just like you. However you can revisit the dungeons you've beaten already and buy the missing stuff later. Next dungeons will be bigger and contain much more loot chests. So in fact there is no need to grind things, but it's up to you :D
And it was a really weird bug with Qaug. Yes, it can't hurt you if you're dashing. Guess you have an inhuman reaction ;)
Looking forward to see your next videos. Cheers!