Index: qemu/vnc.c
===================================================================
--- qemu.orig/vnc.c	2007-12-10 11:39:04.000000000 -0600
+++ qemu/vnc.c	2007-12-10 11:42:57.000000000 -0600
@@ -258,6 +258,13 @@
 
     h += y;
 
+    /* round x down to ensure the loop only spans one 16-pixel block per,
+       iteration.  otherwise, if (x % 16) != 0, the last iteration may span
+       two 16-pixel blocks but we only mark the first as dirty
+    */
+    w += (x % 16);
+    x -= (x % 16);
+
     for (; y < h; y++)
 	for (i = 0; i < w; i += 16)
 	    vnc_set_bit(vs->dirty_row[y], (x + i) / 16);