When you place a structure block, the value of its author tag is set to your name and when you load a structure, the value of the author tag is set to the name of the player who created the structure.
The problem is that if you cycle back to the SAVE mode again and save a structure it still uses the name of the person who created the structure you loaded before.
What I would expect is clicking the "Save" button sets the author tag to your name.
- Place a structure block with the following command and click the "Save" button
- Load the structure
- Save your own structure with the same structure block
- Load your structure in a new structure block
- Run the /blockdata command on the structure block you loaded your structure with
→ It says author:"???"