Done:

When using included S-Lang, don't fill empty areas with spaces (' '),
because they are copied to the buffer when doing cut and paste.

src/TODO

@@ -14,9 +14,6 @@ REGRESSION: Allow minimal functionality on read-only filesystems.
 
 Don't rely on temporary scripts being executable.  Run shell explicitly.
 
-When using included S-Lang, don't fill empty areas with spaces (' '),
-because they are copied to the buffer when doing cut and paste.
-
 Alt-P in the editor should return the viewport to the leftmost position.
 
 Recheck and clean up manuals.  Add node names to the English manual.