Playing with new skills these days, I found another bug related to slider.
Slider -> Shimmier transition fails if the platform is only one pixel thick.
(https://i.imgur.com/rdI9SQA.gif)
As you can see, you can assign shimmier to a sliding lemming, but it doesn't work and he fall down.
But you can get desired result with two shimmiers.
There's no problem if the platform is more than one pixel thick though.
(https://i.imgur.com/hQ16kxE.gif)
(https://i.imgur.com/8VQ3SyQ.png)
I'm sure I remember already fixing this, but maybe not...
I just confirmed that this bug doesn't occur in V7.