This happens on the genuine version too; it's not unique to the NeoLemmix port. When he mentioned that before, I assumed he was talking about not being able to step up them when he should be able to; thus why I got confused and thought it was the same issue.
On a side note, I've looked at the other two issues listed under known issues:
- The objects not getting "no overwrite" properly: This is actually a difference between the true Copycat Lemmings levels and the Cheapo versions of them these were based on. And in fact; this trap not working (the one in Fun 12) is also an issue that's also present in the Cheapo versions of these levels, but not the genuine Copycat Lemmings. Thus, I guess there's nothing wrong with the code setup that was making this trap not work; instead this level is what's faulty - my initial method of "just move the trigger area down by one pixel" is perfectly fine!
- The horizontal flip issue, I still haven't come under any cases where this affects any Copycat Lemmings levels; regardless, I've added code to work around this issue as I can almost guarantee there will be Cheapo levels where this does come up involving custom styles (or possibly even the ONML ones).
EDIT: The first point, on even closer investigation, it appears the issue with Fun 12's trap might actually be with a difference in this object's trigger area between Copycat and Cheapo.