[disqard]

The character sometimes passes (horizontally and vertically) through walls/ceilings, and I can't seem to control when this behavior occurs.

Is there a special game mechanic in this platformer?

[zamfofex]

If a platform is one tile tall, it will act as a semi‐solid that you can jump up through. If that’s not what you mean, then any kind of evidence (like a video or a screenshot) or some description about what you were doing that caused it would be very helpful!