Using 2.38 with a number of tags loaded (so the horizontal scrollbar appears), scroll to the right so that the Artist column is still visible. Click on a song and then click again on the artist cell for that song to begin editing it. If you wait ~1 second, the scrollbar will jump back to the left and you'll be left with two edit boxes on the screen, really screwing up the display.
unfortunately, I can't reproduce it here. What version of Windows are you using?
I'm using Vista (32-bit).
This should be fixed with Mp3tag v2.39.
Thanks for reporting!