I can reproduce this one pretty consistently, so it's quite possibly been fixed in your dev branch already. Lay out a building. Place some modules. Save and exit. Load the save. Use the Modules -> Dismantle Module button to cancel one of the not-yet-built modules. When you hit the Modules button to place more modules, the building's base is no longer shown (whether it would be red or blue). See attached screenshot.
Oh, does this only show up when loading a save? I've been trying to figure out how to reproduce it consistently.
