From time to time--not super often, but often enough to warrant comment--I'll have a ship stop dead in its track...and refuse to move.
Nothing I do will make it budge. I can turn, I can fire, but moving forward has ceased to be an option.
This ability will be restored as soon as my current, unmoving ship is destroyed, but until that happens, even if I destroy an enemy ship in between stopping and dying (which has happened, but it's not easy), I cannot propel my ship.
It seems to happen most with larger ships; I don't recall it ever happening with something flea-sized...though it's possible I just don't recall or haven't had it happen despite it being a possibility.