It looks like a gstreamer bug.
Have you activated the gapless option ? (look for the "advanced options" button in the audio tab) Try without gapless if it was checked.
You can try reproducing the bug with this sample program : https://gist.github.com/squentin/1f28395c4e2a9dac0bee (quickly made mostly from copying bits of gmusicbrowser_gstreamer-1.x.pm)
run it with a few m4a files as arguments and let it play.
Have you activated the gapless option ? (look for the "advanced options" button in the audio tab) Try without gapless if it was checked.
You can try reproducing the bug with this sample program : https://gist.github.com/squentin/1f28395c4e2a9dac0bee (quickly made mostly from copying bits of gmusicbrowser_gstreamer-1.x.pm)
run it with a few m4a files as arguments and let it play.