Update: This doesn't work for fonts that use the right-most column. In fact the issue seems to be cleartype writing outside the leftmost pixel in the bounding box. :-(
Here's a fix for this super-annoying bug (Lucida Console 11, insert spaces before the C to leave a trail of cleartype pixels).
=================================================================== --- gui_w32.c (revision 1289) +++ gui_w32.c (working copy) @@ -2234,6 +2234,8 @@ * Note: FillRect() excludes right and bottom of rectangle. */ rc.left = FILL_X(col); + if (rc.left > 0) + --rc.left; rc.top = FILL_Y(row); #ifdef FEAT_MBYTE if (has_mbyte)