pause to play hangs

[Marco Trapanese]

Hello,
I have a playbin pipeline in C++.
I created this two functions:

void QPlayer::pause() {
     if (m_pipeline) gst_element_set_state(GST_ELEMENT(m_pipeline), 
GST_STATE_PAUSED);
}

void QPlayer::resume(){
     if (m_pipeline) gst_element_set_state(GST_ELEMENT(m_pipeline), 
GST_STATE_PLAYING);
}


in order to pause and restart the video playing.
It works but sometime when I switch back to the PLAYING state the video 
hangs.

What's the right way to pause and restart a pipeline?
Thanks!
Marco