I have built gnuplot from cvs source (the last ChangeLog date 2014-03-07).
The qt terminal has been built and has been set to default.
In the plotting on qt terminal, I have met the following message and plot has been failed:
Terminal type set to 'qt'
gnuplot> plot sin(x)
Could not connect to gnuplot_qt "qtgnuplot1352" . Starting a new one
Warning: slow font initializationgnuplot> exit