Mask for the curved rail is a bit off and allows to build other things on tracks in three positions, as shown on screenshot by lamps.
Same for their mirrored counterparts.
[16.20] Curved rail mask is a bit off
Re: [16.20] Curved rail mask is a bit off
Thanks for the report however this is simply how it has to work if you want to be able to build curved rails next to each other. The game does not support curved bounding boxes.
If you want to get ahold of me I'm almost always on Discord.