bug#1120: issues on (put 'insert-date 'delete-selection t)

[Richard M. Stallman]

    according to delete-selection-mode's header file, elisp code that  
    insert text that wants to respect delete-selection-mode should set  
    the symbol's delete-selection property to true.

    However, this works only when the command is called by a keyboard,  
    not by M-x.

    This appears to be a bug?

It's intentional.  This feature implements expectations that users
have for single-character editing operations in other editors,
where those commands don't have names and there's nothing like M-x.
So there's no reason why M-x should delete the region.

It is better for M-x just to call the function.