This is best viewed in ZDwars map 27, which I have shoddily ripped a base from so you can observe the HOM effect for yourselves (aside from the other homs since i was too lazy to retexture the base once I ripped it.)
This was fixed in GZdooms OpenGL renderer in version 1.6.0, but ZDoom's software renderer still carries this issue.
A Picture of this Error in OpenGL on Skulltag, but in Zdoom instead of dissapearing they turn into HOMs.
Link to example wad, only pay attention the slopes.
https://dl.dropbox.com/u/86298151/WhyWe ... Things.wad