Using the copy/paste tool from building gadgets mod I noticed an archaeologist NPC and its stone structure get generated into the schematic that was copied in. The build I pasted in had a basement that was pasted into ground in a test world that had 2 blocks of dirt and three blocks of bedrock before going to void (blocks were not destroyed before pasting in). This structure was generated again in a second paste, but I made several more after that around the test world and didn't see it happen again.