[Bug] after demolishing underground signal cabins , you can't restore the land

[johnson2008]

this might or may not be a related issue to: https://forum.simutrans.com/index.php/topic,19461.0.html
unlike the above, I was able to build underground signal boxes (I switched to underground view and clicked anywhere) however after demolishing them a base was left where the signal box was. but I am unable to get rid of it, neither with the bulldozer nor the sliced view tool, nor attempting to terraform near it as it made things worse and left a bump that I can't terraform anymore.
how to possible reproduce:
1. start with a year when the underground signal cabin is available (preferably 1898)
2. switch to underground view (not sliced one)
3. build an underground signal cabin
4. now switch to sliced view and on the current level (one level below where it was built) demolish it
5. you will now realize there is something left called 'Base' (it will be renamed 'Land' when the game is reloaded)
it will now stay here forever, terraforming (Landspace tools) or bulldozer on any level (of sliced view) won't get rid of it
6. in addition try to build down artificial slopes on the same tile, and you will see the error, the land is ruined permanently.