I'm not sure if this is a bug, but I found out that the prism slopes and the prism wedge slopes can only face upwards or downwards (I cannot seem to turn them on their sides).

They don't have code for side-facing orientations. It's a long and tedious process to add new orientations which is why for future slopes I intended to only create one shape for each type and allow rotation. It's only partially done, with absolutely no ETA on completion.

I did see that briefly, a prism slope had rotated to "extend" the side of a block, and then it just snapped back so that it faced up.