perhaps it's 800x600, and X switches to the second metamode?
That was exactly it. I went in and changed the resolution in UT to 1024x768, and it propmptly switched itself back to my monitor.. so basically, when I do something that requires the lower resolution, it will switch to the first available metamode with that resolution. Didn't know it did that.
I took advantage of it, though, by adding a third metamode with 800x600 on my monitor and NULL on the TV, so that those games I have that force me to go to 800x600 can still be played on my monitor. Thanks for the help, y'all.