I tried this patch:

diff -up ./src/gallium/drivers/radeon/radeon_uvd.c.vc1
./src/gallium/drivers/radeon/radeon_uvd.c

--- ./src/gallium/drivers/radeon/radeon_uvd.c.vc1    2013-09-27
23:10:44.292867514 +0200
+++ ./src/gallium/drivers/radeon/radeon_uvd.c    2013-09-27 23:14:45.384398128
+0200
@@ -1094,8 +1094,12 @@ int ruvd_get_video_param(struct pipe_scr
         case PIPE_VIDEO_CODEC_MPEG12:
         case PIPE_VIDEO_CODEC_MPEG4:
         case PIPE_VIDEO_CODEC_MPEG4_AVC:
-        case PIPE_VIDEO_CODEC_VC1:
             return true;
+        case PIPE_VIDEO_CODEC_VC1:
+            /* Only advanced is supported */
+            if (profile == PIPE_VIDEO_PROFILE_VC1_ADVANCED)
+                return true;
+            /* fall through... */
         default:
             return false;
         }

Yet my WMV3 file is still going through VDPAU. So either my file is advanced
profile and that is broken, or xbmc not fully respecting the list?