[PvK]

Simultaneous movement or turn-based?

You say you left ships behind, so I suppose the turn ended with your ships one sector away from the homeworld, ordered the speed-5 fleet to move to the homeworld, and the result was another combat in the intercept sector?

If it was simultaneous mode, it may simply be that the simultaneous event resolver decided there should be another combat round before your speed-5 ships were able to move to the homeworld.

PvK