Alex,
Probably because Click() is just a notification that a MouseDown() and MouseUp() occured on the same object. If you had put code into the MouseDown() and/or MouseUp() you probably would have needed to use the NODEFAULT to prevent the re-execution of the BaseClass behavior from undoing changes done by your overridden code.
>Thank you for the explanation, but why Click does not work the same way ? Shouldn't SelStart be set consistently ?