Vanilla-Behaviour:
1. Create a Structure-Block (Save-Mode) and save an area with some coordinates in there
2. Click Strg + Middle Mousekey and you do the NBT-Copy
3. Place the Structure-Block again and the NBT-Data is cloned

On the spigot-server, step 3 dont work - you get a normal structure block with no NBT-Data in it, even if step 2 worked - you get a structure-block with the violet "+NBT" in the inventory.