No invites after placement

So, the problem is basically this: You make a ranked team. You invite 2 people. You play some 3v3s for fun. You place in your 3v3s. Now suddenly BAM you can't invite anyone else to the team. So, you have a ranked team which has less than 5 people and to which you cannot invite anyone else. So you can't play any summoners rift and there is nothing you can do about it. I don't know if this qualifies as a "bug" exactly but it seems like a pretty big problem caused by a mechanic that was never intended to prevent a team playing 5v5 games. Team should always be able to invite people if they have invited less than 5 people total. To do anything else is crazy. It completely cuts off the most important game mode in LoL for no reason at all.