That image looks like it belongs to a level that has a lot of potential to break software mode... ;-P
Seriously, there are too giant viewfields. You have to cut them smaller with some walls (at best with thok-barriers in their back). If you are exceeding a certain size of a viewfield software won't be able to draw the textures properly anymore. This causes ugly graphical glitches.
So you might say "software mode is WE4K" but not Doombuilder. You can still play these levels in open-GL if you want to get an idea of what it would look like the right way.
Well... since I am not a big fan of OGL I would recommend you to work on your levels a little more to make them software mode suitable.
Like BlueZero4 said it might be some unclosed sector borders, too, but only judging by a screenshot it's really hard to tell.