This has been happening for years and years. It's their method of preventing people from spamming you unsolicited.
actually, i think it might be more about generating revenue for facebook. I've received very little spam in my 'other' box, and a spam filter would probably be pretty effective at reducing that anyway (were it even an issue). I think the spam thing is just an excuse, so facebook can give you the option to pay $1 to get your message to the recipient's regular inbox.
But yeah, this is old news and I'm surprised anyone is just now learning about it.
Holy shit.
Well, there goes all those connections I could've had.
Better destroy your laptop, phone, and wrap the room in foil.