I noticed the attached on map08 of my NJ Zdoom 2001 in the area where you get the yellow key. If rendering is set to quality, the bars "shimmer" between being foggy and non foggy. There is fog on one side of the bars, but not the other.
[edit] Sorry, should have mentioned a version number. I'm not sure exactly when it appeared. However, it doesn't happen with the last official release but it does with recent SVN versions. [/edit]
Yes, I know the problem. It's a bit more complicated than quality vs. speed though and it will have to wait until some more code of the new renderer is done which would make fixing this easier.