Even -nounevenstretch doesn't seem to help. Maybe it's another obscure setting conflicting, or maybe even my wonky ATI card drivers, but this is what I get with -nounevenstretch.
I highlighted two columns that are unevenly stretched with respect to the others. Same thing happens full screen, I just couldn't get a screen grab unless windowed.
You don't tend to notice it in static screens like pacman, but you do in scrolling games like mslugx. You kinda get a "shimmering" effect during the scroll.