Unexpected prompt for new file name when saving after editing a block from the block list

Some days after creating a block, I wanted to make edits. I went to the Block List widget,
selected the named block, and made changes within the block’s dedicated editing frame.

However, when I pressed File > Save, it prompted me to save as a new file instead
of saving automatically in the existing drawing file.  What is the proper procedure to follow
after modifying an existing block?"

Just close the block editing frame and save the main drawing.
The block is kept in memory, because it is part of the DXF and stored with the main drawing.

Using Save in the editing frame gives the opportunity to save the block only as separate DXF file.
This is useful to import the block into another drawing or use it in the library browser.
Thus the dialog asks for the name of the block DXF.