Nortaneous: I have no idea what could cause that issue so suddenly. Perhaps Simon can help you there, he also knows a bit more about how Allegro works I think.
I had actually made triangular pipe pieces in the meantime that could be used as junctions (pretty small ones, so small that the border drawn around them in the editor makes it hard to see how they are oriented), though now that you made these, I can include just these as well, they are probably easier to work with, thanks.
The brazier and torch objects in the sandstone style need to have their transparent pixels sorted out, right now many of the background pixels around the flames are black rather than transparent. In addition to working against non-black backgrounds, it will also become relevant if support is ever added for objects drawn in front of terrain.
Well the thing here is, as I have no partial transparency, I have to pick a color against which to blend it, which obviously has to be black. So even if I give those pixels that are close enough to black full transparency, those that are somewhat lighter will still stand out against a lighter background, as they were blended against black and not that specific background color (you can see this especially well if you have two overlapping buzzsaws, the one with higher priority looks like it has some black border around it). So thinking I can't fix that anyway, I went the lazy route and just kept even the basically transparent pixels black.
If you think making these full transparent though gives an improvement nevertheless, I can do that though. Same with the steam, etc.
in the graphics department, do we have any very thin pieces like those in the marble set of Original Lemmings? So far all I've found is pipes and thin blocks in a few different sets but none are thin enough. I'm trying to make this level that requires some almost exactly like that, and I can't use eraser pieces either (you'd understand if you saw it). I could make the graphics myself I just need to know the instructions on that topic. Can they be made in paint?
Basically, as Proxima said, using eraser pieces should always work, and usually you can even remedy the effect of things looking cut off using the no-overwrite trick.
Anyway, what will be included in the next version (in the construction set) is something resembling a platformer's platform to some extent (both as normal terrain and steel, just like the staircase in that set), so that's about as thin as it reasonably gets. I attached the bitmap file to this post so you can see what I'm talking about.
That said, you can always make your own tiles and ask them to be included if they look decent enough.
I honestly didn't even know the functionality of moving things to front/high priority and back/low priority were called like that. Yeah, something like Proxima suggested seems more appropriate as a name.