Ya the whole thing doesn't make any sense. Is as if they threw strongholds without knowing what they were doing. If you conquer a Planet you should be able to retain it until ist up for grabs again and if you choose to defend it you should be able to. If not, whats the point?
I just logged on today to see that we lost Makeb and it was up for grabs again when there are still 7 more planets that havent even been on rotation yet. You would expect all 15 planets to be able to be conquered first (a cycle) before letting you conquer the same planet after 2 weeks.
I really hope its a bug because conquest wont make any sense at all, flybys, the walker etc. would be pointless.