Issue selection should not cross active sprint/backlog boundary

Steps to reproduce:

1. Select multiple issues at the top of the backlog
2. Create a future sprint, and put the top issue into it
3. Start the future sprint
4. Return to Plan Mode
5. Expand the view of the Active sprint

Expected:

• the issues selection should be cleared each time a sprint is started*

Actual:

• all issues from original selection are still selected.