trying to achieve playbin2 gapless transition

[Captian Ham]

To get acquainted with gstreamer I'm writing (what I would assume to be) a
very simple program to play a succession of media files (pictures and
videos); when I transition between files I'd like the frame of the last file
to freeze in place until the next file starts playing. I'm using playbin2
with an xvimagesink linked to a gtk window to display the output. My
understanding of the process is to handle the transition like this:

gst_element_set_locked_state( xvimagesink_, TRUE );
gst_element_set_state( playbin2_, GST_STATE_READY );
g_object_set( G_OBJECT( playbin2_ ), "uri", newfile_.c_str(), NULL );
gst_element_set_state( playbin2_, GST_STATE_PLAYING );
gst_element_set_locked_state( xvimagesink_, FALSE );

And while this seems to work exactly as intended initially, after about
ten/twenty transitions it deadlocks without fail on the GST_STATE_READY call
to the playbin2 element: 

#0  0x0012d422 in __kernel_vsyscall ()
#1  0x00df7af9 in __lll_lock_wait () at
../nptl/sysdeps/unix/sysv/linux/i386/i686/../i486/lowlevellock.S:142
#2  0x00df313b in _L_lock_748 () from /lib/tls/i686/cmov/libpthread.so.0
#3  0x00df2f61 in __pthread_mutex_lock (mutex=0x826225c) at
pthread_mutex_lock.c:61
#4  0x00c7283e in g_static_rec_mutex_lock () from /lib/libglib-2.0.so.0
#5  0x013c8421 in ?? () from /usr/lib/libgstbase-0.10.so.0
#6  0x013c9814 in ?? () from /usr/lib/libgstbase-0.10.so.0
#7  0x0032900f in gst_pad_activate_push () from
/usr/lib/libgstreamer-0.10.so.0
#8  0x00329d98 in gst_pad_set_active () from /usr/lib/libgstreamer-0.10.so.0
#9  0x0030815b in ?? () from /usr/lib/libgstreamer-0.10.so.0
#10 0x0031a9f7 in gst_iterator_fold () from /usr/lib/libgstreamer-0.10.so.0
#11 0x0030808f in ?? () from /usr/lib/libgstreamer-0.10.so.0
#12 0x0030a6f8 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#13 0x0030cc19 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#14 0x00309435 in gst_element_change_state () from
/usr/lib/libgstreamer-0.10.so.0
#15 0x0030c928 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#16 0x003087f0 in gst_element_set_state () from
/usr/lib/libgstreamer-0.10.so.0
#17 0x002f8827 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#18 0x00309435 in gst_element_change_state () from
/usr/lib/libgstreamer-0.10.so.0
#19 0x0030c928 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#20 0x003087f0 in gst_element_set_state () from
/usr/lib/libgstreamer-0.10.so.0
#21 0x002f8827 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#22 0x0136acfa in ?? () from /usr/lib/gstreamer-0.10/libgstplaybin.so
#23 0x00309435 in gst_element_change_state () from
/usr/lib/libgstreamer-0.10.so.0
#24 0x0030c928 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#25 0x003087f0 in gst_element_set_state () from
/usr/lib/libgstreamer-0.10.so.0
#26 0x002f8827 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#27 0x0032cdf2 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#28 0x013615ba in ?? () from /usr/lib/gstreamer-0.10/libgstplaybin.so
#29 0x00309435 in gst_element_change_state () from
/usr/lib/libgstreamer-0.10.so.0
#30 0x0030922e in gst_element_continue_state () from
/usr/lib/libgstreamer-0.10.so.0
#31 0x003094bf in gst_element_change_state () from
/usr/lib/libgstreamer-0.10.so.0
#32 0x0030c928 in ?? () from /usr/lib/libgstreamer-0.10.so.0
#33 0x003087f0 in gst_element_set_state () from
/usr/lib/libgstreamer-0.10.so.0

No deadlock occurs if I don't lock xvimagesink first. I'd appreciate some
guidance on; why locking a child element might cause a state change to a
parent to fail? Why does locking in this way produce a volatile outcome that
fails every now and then? Is this the most sensible approach to simple
"gapless" transition between media with using a playbin2 pipeline.

Thanks in advance,
CH

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