So when you have some drones for a capital ship (like Behemoth), they auto-deploy when you need repairs and if in travel mode, you will quickly loose them (you see them trying to follow close but they finally get lost). This also happens with AI controlled ships (at least when in same sector, havent checked when OOS). So basically either dont assign repair drones to a ship if you plan using travel mode
or be ready to loose a lot of them, so erm yes that's a bug right 