I was just trying to do some cleanup in one of the rooms I frequent - we've got a bot that posts comments into the room at times, and so I was trying to remove the messages that didn't need to be there anymore (especially since some of them had tripped the "offensive" filter and so there was no need to leave them around).
So, to easily find just the bot's messages, I hid everyone else's messages temporarily, so only my messages and the bot's were visible to me. I then selected the messages using the shift and ctrl buttons that you can use to select messages when moving.
Unfortunately, hiding the posts didn't mean that they weren't selected when I used shift. This resulted in... a bit of an accident where I accidentally moved 300 messages to another room (which I then fixed).
But this wouldn't have happened if it didn't move messages that weren't visible to the one moving. If the one moving the messages can't see the messages, then don't move the ones they can't see, to prevent mishaps like this in the future. (I assume this works the same way for people that you're ignoring, but I haven't tested.)
So can ROs and mods please not be able to move messages that they can't see?