How to reproduce this bug:
Select Save As
in the Save As dialog select an existing file, so that the file name appears in the filename input box and you can edit it
Edit it by pasting the content of the clipboard with CTRL-V
Press save and a warning dialog warns you that if you save you would overwrite the selected file, even if the input box shows a different name
From what I can see, the problem is that CTRL-V doesn't remove the focus from the selected filename, thing that correctly happens if you edit the filename by manually typing a character.
Windows XP SP2