I wonder if your virtual desktop resolution is larger than the actual resolution you use.
For instance if your X setup can go 1024x768 but you run tv-out and freevo in 800x600, X will make a virtual resolution of 1024x768 so that the desktop can be scrolled. Maybe this is related to your problem?
My experience with freevo is that it works best with a separate specialized X setup, so that you can force X into a specific resolution. You can have several Screen sections in your XF86Config-4 and then chose between them when X is started.
I used to run Freevo like that in another VT, but after getting an Nvidia card my tv-out doesn't work at all, so I haven't tried if this works well with the nvidia drivers.
By the way I agree that Freevo is really cool.