no, these happen sometimes, i get it alot. i told a bunch of new caps to join a fleet, and to get to the fleet they had to jump through a wormhole. however, once they got to the wormhole, instead of using it, they decided to use sub-light engines to get to the other wormhole (yes, i had all the necessary tech researched).
another time i was re-inforcing a fleet at one planet. as it was building i went away and did other stuff, but the pips at the first planet stayed there the entire time. eventually, when the fleet finished building, i zoomed in to have a look, and it wasnt in the GW, anywhere. i zoomed out, moved the camera around. it turned out the fleet had spontaneously decided to fly 'north' (upwards, basically) and by the time i got there they were about 20 mins worth of sub-light time out of the GW. in the end i just scuttled the fleet and started again.
im fairly sure its a bug, but it only happens sometimes so there must be a funny contradiction somewhere in the code.