For some reason Octave's plotting capability seems to be broken down. I can reproduce this on two machines running Fedora 21.

In a clean environment, starting Octave and running a plot results in a segfault

octave:1> x=0:.01:2*pi;
octave:2> plot(x,sin(x));
panic: Segmentation fault -- stopping myself...
attempting to save variables to 'octave-workspace'...
save to 'octave-workspace' complete
Segmentation fault (core dumped)

This also happens with

octave:1> graphics_toolkit("fltk");
octave:2> x=0:.01:10;
octave:3> plot(x,sin(x))
panic: Segmentation fault -- stopping myself...
attempting to save variables to 'octave-workspace'...
save to 'octave-workspace' complete
Segmentation fault (core dumped)

but with gnuplot it works

octave:1> graphics_toolkit("gnuplot");
octave:2> x=0:.01:10;
octave:3> plot(x,sin(x));
octave:4>

Could it be that fltk's ABI has been broken?