Bottom edge of the update region should be relative to the top edge of
the format rect.

diff --git a/dlls/user/edit.c b/dlls/user/edit.c
index 1f7ecbb..e9973b6 100644
--- a/dlls/user/edit.c
+++ b/dlls/user/edit.c
@@ -1282,6 +1282,7 @@
 			rc.bottom = line_count * es->line_height;
 		else
 			rc.bottom = line_index * es->line_height;
+		rc.bottom += es->format_rect.top;
 		rc.bottom -= (es->y_offset * es->line_height); /* Adjust for vertical scrollbar */
 		tmphrgn = CreateRectRgn(rc.left, rc.top, rc.right, rc.bottom);
 		CombineRgn(hrgn, hrgn, tmphrgn, RGN_OR);