http://code.google.com/p/webm/issues/detail?id=371
https://hg.mozilla.org/mozilla-central/raw-rev/bc3fe56d732d
https://gerrit.chromium.org/gerrit/#change,10925

--- vp8/decoder/decodemv.c	2011-08-15 21:02:45.000000000 +0000
+++ vp8/decoder/decodemv.c.oden	2012-02-27 09:13:32.000000000 +0000
@@ -322,6 +322,7 @@ static void read_mb_modes_mv(VP8D_COMP *
             const int num_p = vp8_mbsplit_count [s];
             int j = 0;
 
+            mbmi->need_to_clamp_mvs = 0;
             do  /* for each subset j */
             {
                 int_mv leftmv, abovemv;
@@ -366,7 +367,7 @@ static void read_mb_modes_mv(VP8D_COMP *
                     break;
                 }
 
-                mbmi->need_to_clamp_mvs = vp8_check_mv_bounds(&blockmv,
+                mbmi->need_to_clamp_mvs |= vp8_check_mv_bounds(&blockmv,
                                                           mb_to_left_edge,
                                                           mb_to_right_edge,
                                                           mb_to_top_edge,