Steps to reproduce:
1) Assign a Stacker.
2) Make a lemming a Climber so that he can climb the stack.
3) Assign a Shimmier to the lemming while climbing the stack. At one point, he can transition into a Shimmier (i.e. turn around and shimmy into the opposite direction) as if there were a ceiling, even though there is none. It will only be for a very short time, but it can be used to turn a Climber around who would otherwise just climb straight over the stack.
I discovered this behaviour because some people kept using it to backroute some of my Lemmings Open Air levels.
I'm not calling for it to be abolished simply because I want those backroutes broken. In fact, I'm not sure whether I'd personally want to see it abolished at all, because it's a pretty cool trick once you know about it.
The question is just: Is it intentional? And more importantly, would this be in line with what you'd expect? Because it definitely wasn't expected for me at all.
Wouldn't this then also mean that there's a certain point when climbing regular walls where the lemming can transition into a Shimmier, even without a ceiling being there?