I'm using Ultimate Doom Builder.
I have been having issues with a level using slopes and 3d floors to create a beveled area. Looking into this on my own, I learned how to align control sectors and set plane align linedefs to set the slope for the upper part of the beveled area.
The bottom part is set with a slope thing on the playable sector. Here is the result

In the editor, the area above this, where the players start looks pretty trashy, so I use the hotkey in Ultimate Doom Builder to turn off enhanced rendering so that I can see the player starts

Enhanced Rendering On

Enhanced Rendering Off
It plays great in Zandronum, so I was pretty happy. Here's a WAD : Working.WAD
Then I continued to edit the level and add monsters / other details. Eventually the thing borked, and I can not find the reason. Here is my current busted WAD, where it is rendering in game the nasty way that it looks in enhanced rendering mode : Broken.WAD
Why did this work before, and then break? What can I do to fix it? Pretty lost. Thanks in advance for anybody who finds the time to add your 2 cents