Unkillable girl on the Parade corridor - "About the invincible child, it's most certainly a bug. You see, every one of those have a specific flag to tell the game they're dead (313,314,315…). That child in particular activates flag 315 but checks flag 314 to see if it died. If you kill the grey-haired child below the door, which activates flag 314, then the invincible child will die as well"
Taken from http://archive.uboachan.net/flow/res/1097.xhtml#1782
Demons on the Rust Corrupted School event don't harm Sabitsuki - "Also, to shine some light on that. I know I talked about how they did nothing on a previous post, but those Rust Corrupted School demons are supposed to do something. Their coding is different from other demons, in that a single touch would kill Sabitsuki, instead of needing 15 demons (thus explaining their huge size). The only thing that causes them not to do anything is a bug. You see, in all demons, there is a condition that gets checked before they corrupt you, which is whether or not you have the menu commands enabled. Why, I do not know, as I can't remember a situation where the demons and a lack of menu capabilities would conflict with each other. The fact is, this piece of code is still present in the Rust chase sequence's demons, and as we all know well, we can't access the menu in this part, so they do nothing"
Taken from http://archive.uboachan.net/flow/res/1097.xhtml#1667