Tim Peters writes:

I'm still unsure, but couldn't stand the virtual event trickery so tried a
different sin (adding undo_block_start/stop methods to the Text instance in
EditorWindow.py).  Like it or not, it's efficient and works <wink>.  Better
idea?

Give the attached a whirl.  Even if you hate the implementation, I think
you'll like the results.  Think I caught all the "block edit" cmds,
including Format Paragraph, plus subtler ones involving smart indents and
backspacing.

Tools/idle/FormatParagraph.py

@@ -37,8 +37,10 @@ class FormatParagraph:
         text.tag_remove("sel", "1.0", "end")
         if newdata != data:
             text.mark_set("insert", first)
+            text.undo_block_start()
             text.delete(first, last)
             text.insert(first, newdata)
+            text.undo_block_stop()
         else:
             text.mark_set("insert", last)
         text.see("insert")