Hovering fleet should be able to attack the planet as it is no longer under your control.
Fleet hovers with nothing to do, and can only be recalled.
I think it does this because because station fleet don’t require trannies (which is weird).
Stationing fleet does not require transports since your units are being transferred to their destination using logistic spacecrafts. Unlike the military designed transport that can carry 100 units max - the logistic spacecrafts can carry thousands of ground units. Those logistic spacecrafts are not designed for battle, they have very low defense and can be easily hunted by enemy fighters due to it’s big size and low maneuvering capabilities and losing it will cause loses of thousands of ground units per ship.
Needless to say that the logistic transfer of units is very different than the military transfer which allows units to prepare for battle and deploy in combat mode. Landing ground units from logistic spacecrafts into battle is nearly impossible and in most cases will result in the destruction of the spacecraft from enemy ground fire before the units inside will manage to deploy and prepare themselves to battle.
The truth about what happens and the real bug:
When a reinforcement is sent to a planet and the planet changes ownership - the reinforcements are recalled to the main fleet immediately.
The real bug is that they keep showing as hovering even though they are not because the reinforcements protocols are still not complete and for some reason the report of the returning forces is not updated in the main fleet (even though the forces are already returned!) therefor the emperor sees it as if the forces are still outside and not updated in the correct fleet situation until the fleet commanders manually update it.
It’s all bureaucracy and broken protocols, everything is fine besides that 
a clever take! blame the bureaucrats, i like it 