I tried playing with the platforms a bit and it seems that they still try to spawn as if it's a horizontal level, meaning they can only actually spawn on screens 00 or 01 (with a reflection of their LM position across y=x). I can't find a disassembly, though, so you'd have to search all.log for the offending line of code.
Professional frame-by-frame time wizard. YouTube - Twitter - SMW Glitch List - SMW Randomizer