As we can see here: https://jenkins.arracacha.collabora.co.uk/job/gst-validate-tests/898/testReport/ tests that have a timeoverlay and a videomixer (compositor or old school videomixer) fail to negotiate.

Reproduction:

gst-launch compositor sink_1::alpha=0.5 sink_1::xpos=50 sink_1::ypos=50 name=_mixer !  deinterlace ! videoconvert ! 'fakesink' videotestsrc pattern=snow timestamp-offset=3000000000 ! 'video/x-raw,format=AYUV,width=640,height=480,framerate=(fraction)30/1' !  timeoverlay ! _mixer.

or

gst-launch videomixer sink_1::alpha=0.5 sink_1::xpos=50 sink_1::ypos=50 name=_mixer !  deinterlace ! videoconvert ! 'fakesink' videotestsrc pattern=snow timestamp-offset=3000000000 ! 'video/x-raw,format=AYUV,width=640,height=480,framerate=(fraction)30/1' !  timeoverlay ! _mixer.


The culpright commit is:

commit 76ce11299411b412702d3fab34b7f152dc211156
Author: Arnaud Vrac <avrac@freebox.fr>
Date:   Thu Sep 4 15:06:31 2014 +0200

    basetextoverlay: schedule reconfigure on source pad when negotiation fails
    
    The source pad might be flushing while negotiating, resulting in
    set_caps or the ALLOCATION query failing. In this case set the
    reconfigure flag on the source pad so that negotiation is retried on the
    next buffer.