I've been working on this one for a while.
The symptom is this:
A blank white screen is fine.
A blank white screen with text generates a line
the height of the text which extends the horizontal length of the screen. It comes out lighter than the text (for black, it's a gray smear).
I'm apparently not the only one with this problem, judging by http://www.nocrash.com/ncbbs/msgs/157.shtml
and other research on the web, but I haven't found a solution.
I get this effect in every screen mode, including the BIOS setup screen.
How can I resolve this?