I've tried removing the green curbs from a yellow road booster in the mesh modeler the other day and after saving the new block, it added a random turbine spinning next to it.

It's not visible or clickable in the mesh modeler whatsoever.
The bug is reproducable, here's a video of what I've done to get it:
https://streamable.com/63ro6
I uploaded this for taxon because he seemingly can't post links or images in the forum.