The bug has been opened on https://bugs.launchpad.net/bugs/138001

"...
just move the slider, sometime when I release the mouse click the slider continue to move.
...
it happen when I release the mouse click outside the slider area, for
example, on the visualisation. Sometime it works normaly, sometime, the
slider is released 2 or 3 secondes after I release the mouse button, and
sometime he isnt released at all.
It happen with audio and video. To trigger the bug I need to move the slider
really fast.

it look like GTK_UPDATE_CONTINUOUS is used, but GTK_UPDATE_DELAYED would be
better. and the continuous update send lot of update order, that gstreamer
cant satisfy. so it lag, and I can continue to move the slider after the
mouse button is release. Most of the time for 4 or 5 secondes after the
button release.

I use totem-gstreamer
..."