[xmonad] Windows Extending to Both Monitors in a Dual Monitor Setup

Hi, I've been using xmonad for some time, and I've never seen this problem before. I'm using it on my laptop, which I sometimes connect to a projector or to a monitor using a dock. This has always worked fine. However, a few days ago, it suddenly started stretching my windows across both monitors instead of keeping them tiled on one or the other. It's as if xmonad thinks I actually have one really wide monitor instead of two. I'm not sure where to start looking to fix this, since I didn't really change anything significant of late. If anyone can point me in any useful direction, I would really appreciate it. Thank you, -- There are 10 types of people, those who know binary and those who don't.