Midtexture alignment?

I think this is probably a case of issue #2 here: Vertical offsets are ignored in texture patches. You can make sure the texture's patch does not have a vertical offset, or use ZMAPINFO to set the corresponding compatibility option in ZDoom ports.

If the texture patch's Y offset is already 0, then I don't know.

Are the ceiling heights different on the two sides of that line?  Maybe the renderers have different interpretations of what is the top of the line, or maybe my guess is just wrong.

12 minutes ago, Empyre said:

Are the ceiling heights different on the two sides of that line?  Maybe the renderers have different interpretations of what is the top of the line, or maybe my guess is just wrong.

Hm, nope, the line does not border another sector.

7 hours ago, Gez said:

I think this is probably a case of issue #2 here: Vertical offsets are ignored in texture patches. You can make sure the texture's patch does not have a vertical offset, or use ZMAPINFO to set the corresponding compatibility option in ZDoom ports.

 

If the texture patch's Y offset is already 0, then I don't know.

Thanks, the patch offset was indeed the cause!