Floating Concrete item prevents from placing farm tile

Issue description

There's a floating tile I cannot remove through digging or deletion

Reproduction steps

I believe this was caused by a collapsing building

Game version and build number

v0.7.9a (b500)

Operating system

Windows

Attachments

Save game attached here (would not upload): https://drive.google.com/file/d/1WzzwbjdUbgGyr2-Tz2k0ABg1I8uhvL_d/view?usp=sharing

A similar issue happens if you place a surface on angled terrain when the angle changes after the surface is placed. I was able to dump underneath it to eventually remove the surface, but I suspect it's the same underlying issue.

Step 1.
Place angled surface

Step 2.
(Accidentally) place barrier on the angled surface which flattens the terrain

Step 3.
Notice that the surface is no longer conforming to the adjusted terrain (floating) and cannot be removed