My apologies, I looked into the issue and fixed it. Taking the chance, I also checked all the other riddles, etc. in that area and was able to fix a few other things in the process.
I just did a test play and everything works as intended now. :)
As for the weird walking monster sprites, sadly this is no bug. I'm lacking their respective 4-directional sprites. That's why I decided to turn the direction fix on, because otherwise, the monsters would just vanish as soon as they move in another direction and are invisible.