Duplicate sprint names creating conflicts

Hi,
I have a main agile board which displays the current and future sprints inline for the sub-boards for my Project. Now if I create a new sprint from my main board it gets displayed in my sub-boards. But when i create sprint on my sub-boards it creates the next future sprint number on my sub-board and it gets displayed on my main board with the future sprint number which is a duplicate of already created future sprint in main board. For e.g. i created a future sprint SP-18 on my main board, then i went to one of my sub-boards and created another sprint SP-18 and assigned 1 issue from backlog to it. Now it gets displayed on my main board as SP-18 with the issue attached. I now have 2 SP-18.
Please help me resolve this conflict. It should not allow creation of same sprints which are already created.