Camera can get "attached" to one side of the map or the corner

I've been going over this for a while now, and can't figure out what would cause the camera to "snap" to a position. I have the x, y, and delta values printing to the Console on each "up" movement, and all three show non-zero values, but the camera doesn't move. Snapping it back to the "center" (also not quite right), by pressing x gets out of the stuck condition.
