Steps to reproduce:
1. Do the following pipeline:
gst-launch-0.10 videotestsrc num-buffers=200 !
video/x-raw-yuv,format=\(fourcc\)I420,width=176,height=144 ! ffenc_h263 !
ffdec_h263 ! ffmpegcolorspace ! ximagesink 
2. If I replace ximagesink with aasink or xvimagesink everything works as
expected. Also if I use ffdec_h263 with theora everything works fine

So I am not sure whether the problem is on ffdec_h263 on ximagesink.

Stack trace:
LOG   (0x8052230 - 0:00:08.708773000)      GST_REFCOUNTING(19626)
gstobject.c(398):gst_object_unref:<pipeline0> 0x807b310 unref 3->2
LOG   (0x8052230 - 0:00:08.709243000)      GST_REFCOUNTING(19626)
gstobject.c(398):gst_object_unref:<videotestsrc0> 0x806e568 unref 3->2
ERROR: from element /pipeline0/videotestsrc0: Internal data flow error.
Additional debug info:
gstbasesrc.c(1315): gst_base_src_loop: /pipeline0/videotestsrc0:
streaming task paused, reason not-negotiated
LOG   (0x8052230 - 0:00:08.710600000)      GST_REFCOUNTING(19626)
gstminiobject.c(293):gst_mini_object_unref: 0x8052098 unref 1->0
LOG   (0x8052230 - 0:00:08.710986000)          GST_MESSAGE(19626)
gstmessage.c(210):gst_message_finalize: finalize message 0x8052098
LOG   (0x8052230 - 0:00:08.711465000)      GST_REFCOUNTING(19626)
gstobject.c(398):gst_object_unref:<videotestsrc0> 0x806e568 unref 2->1
LOG   (0x8052230 - 0:00:08.711996000)      GST_REFCOUNTING(19626)
gstobject.c(398):gst_object_unref:<bus1> 0x8113428 unref 2->1
ERROR: pipeline doesn't want to preroll.
Setting pipeline to PAUSED ...

Other information: