The collision data itself is split like that (top solid in one bit, left/right/bottom solid in the other bit), so it can't do otherwise. But the way the check is done also matters -- finding walls check horizontally in collision data, finding ceilings check vertically up, etc.
I apologize for necro-bumping, but there is a fix that, while small, should be reported and fixed in the GitHub disasm. I am not familiar with how the pull requests work so maybe Clownacy or someone can tackle this. In Scrap Brain Act 1, one of the background tiles is mirrored for some reason, resulting in the background looking a bit off in some spots. It is chunk $B5. Thankfully the fix is super simple. In sonLvl, go to the Art Tab and select that chunk and hit Flip Horizontally. The background should look exactly as it should now. I thought of just pushing this to basic Q/A but since it's pertaining to this disasm and will affect anyone using it as a base, I decided this was the best course of action so that everyone who uses this as a base can be informed.
Out of interest, could you provide a screenshot? I believe you, I just cannot quite see it myself, so it must be one of those "you have to know specifically where to see it" and "once you see it you can't unsee it" type of deals, and it would be nice to see where I fucked up d=
Images from Dropbox dont seem to embed. I'm sorry. I provided links though. https://www.dropbox.com/s/yfivq8dhgp3xw8z/Screenshot 2020-05-09 07.25.26.png?dl=0 Here is the one I noticed, that is certainly in the 1 Two-Eight ROM. It's Chunk B5. Mirroring it horizontally fixed this. https://www.dropbox.com/s/7c59dk0k4c8d5t5/Screenshot 2020-05-09 07.25.18.png?dl=0 I didn't notice this one before, so it's possible this one is due to my own mistake (I'm using a touch mouse after all) But it's worth double checking. This one doesn't need to be flipped, but in my build it seems to be missing a cloud block on the very top left. The block that SHOULD be $246 is missing for some reason. Again, could be my error on this one but please double check to be certain.
It looks fine on the original 2010 release of Two-Eight, it matches the original game. I suspect it's either you, or it's on the GIT as well and whoever's contributing to it has screwed it up.
