Issue Summary

Sprints can show up on multiple boards and that's expected.

When only the subtaks of a sprint match another board's filter, though, that sprint doesn't show up in the UI, but shows in the API endpoint /rest/agile/1.0/board/{boardId}/sprint

Steps to Reproduce

1. Create two boards with mutually exclusive filters. For example, one filters the Fix Version 2.0 and the other, 3.0
2. Create a sprint "2.0 Sprint 1"
3. Add a Story with a subtask to it
4. Change the subtask version to 3.0
5. Check the board for version 3.0
6. Run the REST API call to board to version 3.0

Expected Results

The REST API sprints are consistent with the UI.

Actual Results

The REST API shows "2.0 Sprint 1", but the UI doesn't.

Workaround

Search for the subtasks in the sprint and make the appropriate changes so they don't show up in the other board.
This could involve either editing the subtasks or the board filter.