Ok so I've had some good runs, but the ring gets stuck if you throw it and don't retrieve it before entering another room. You will just hear lots of bouncing noises, and you won't be able to throw, effectively losing you the game. I've lost so many rune due to this.
So far, I've only been unable to use my weapon if I didn't pick it up in a previous room. No problem if I remembered to recall it before transitioning.
Recall is assumed to be at fault here because of the above mentioned bouncing noises upon pressing the attack button—apparently from the ring(s) hitting a nearby wall, trying to return to you.
In my testing up to now, two factors seemed to play a big role in the bug:
a) Firing a shot in the room with the stairs and not recalling it leaves me unable to shoot in the next level's starting room (the one with the little pedestal) in 100% of the cases, leading to the known bouncing sounds. Everything resumes working correctly once I enter any connecting room.
b) Performing at least one ”Rite of Multiplication“ is guaranteed to leave me defenseless in an enemy room if I left my rings behind in the directly preceding one on the same floor or the stairs room on the preceding floor. The latter scenario trumps what I described in a). Failing to recall multiple rings in the last room of the previous floor completely locked my out of firing in the next arena, even though I crossed an empty room (start of the current floor) beforehand.
When you get enough of the size increases you get that same sound if it happens to be on the other side of the doorway. It slowly collisions its way back to you with the same bonking on the wall sound. Dunno if it sometimes resets to some default position outside the playfield or whatever. Good finds, hope there will be a new version since I like using the multi power up. Skipped taking those and made it to like level 11 or so before a legit death.