The pipeline consists of filesrc, mpegdemux, and fakesink for each pad created
by mpegdemux. The pipeline is in PLAYING state. When I call gst_element_seek
with element = pipeline and flags = GST_SEEK_FLAG_FLUSH, the pipeline stops forever.

The function do_pipeline seek changes the state to PAUSED before sending the
event and changes the state to PLAYING again. That's OK. But when the fake sinks
get the flush event they call gst_element_lost_state which sets pending =
current state (= PAUSED) and return value to async. The pipeline sets these
values accordingly. Then the pending state is set to PLAYING. But the current
state of the pipeline is never set to PLAYING, its state remains in the
PAUSED->PLAYING transition.