This happened a few times, i had a fleet and told them to fly through a wormhole. The other end was on the other end of the map, but instead of flying through the wormhole, my fleet tried to get there on sublight engines... luckily i caught them before they got too far away but damn....
also, i had a fleet going through two stars to line up for an attack, but when the majority of the fleet got to the second star, it started flying to planetary north (i.e. the top of the sun and beyond)
anyone know why?