When v4l2sink is raised to a non-null rank (because system has a v4l2 output device) and when playbin2 plays back a mpeg-ts file, it ends up auto-plugging the mpeg-ts stream directly to v4l2sink.

This is because v4l2sink unconditionally accepts video/mpegts and doesn't check whether the hardware can actually support it.

The culprit seems to be in gstv4l2object:
@@ -1842,6 +1863,9 @@ gst_v4l2_object_set_format (GstV4l2Object * v4l2object, guint32 pixelformat,
   memset (&format, 0x00, sizeof (struct v4l2_format));
   format.type = v4l2object->type;
 
+  if (pixelformat == GST_MAKE_FOURCC ('M', 'P', 'E', 'G'))
+    return TRUE;
+
   if (v4l2_ioctl (fd, VIDIOC_G_FMT, &format) < 0)
     goto get_fmt_failed;