When using the Polyobj DoorSlide function, I have noticed that Vavoom's distance calculations are seriously messed up.
Regardless of what you set it to, after using the door several times (sometimes even the first time), sometimes it will only partially close, leaving a gap. Other times, it will go too far, and leave a gap on the other side.
I've been able to get a door to only close half way after opening and closing it a few times.
If you want me to, I can set up an example wad for you.