Grass render inside building

When building and placing down a foundation/framework, grass seems to inconsistently render inside the building.


When first placing down foundations the grass would disappear as expected.
Later on when progressing the framework by adding materials the grass would grow through certain foundations.


Destroying and rebuilding foundations gives mixed and varying results. The grass disappears beneath one but stays visible through others. I repeated this a few times with varying results in terms of which foundations stay clear and which don't.


After getting it to disappear completely again I proceeded to finish the building. The grass grows back again.