rock base doors and doorways?

Hello im not sure if the rock creation I found on the map I play on is bugged or Im doing something wrong. I found a giant rock that is hollowed out and plenty of room for foundations on the inside. Only problem is once I place a foundation and a door way, then try to place a door in the doorway they are always greyed out, I tried replacing the foundation and everything, not sure if this is meant to be this way or im doing something wrong, or its bugged? has any one else come across this issue?

It’s bugged :frowning: I posted the other day and it seems a few people have had the same issue.