All I did was make a new cell, leaving all it's values at default, then copied vault 11's gear door along with it's door switches and klaxon, changed it's NIF to change it's texture (blank door from FO3 mod resource), create some more tunnels and add a few mats. Then I created a door randomly in goodsprings to connect to a door in the tunnels to test it. Now when I went into the vault the door worked and everything seems right, except:

It's just that every save I make inside that interior is corrupt. I can save all I want outside of that particular interior cell and it works just fine.

Any ideas why this happens and/or how I can fix this?

ugh... it's because i didn't give the cell an in-game name. i'm stupid.