Closing an issue in a planned (unstarted) sprint does not remove it from the sprint, causing errors when deleting the sprint

Reproduction:

1. Create a new sprint
2. Create an issue and drag it into the new sprint
3. Close the issue. The issue will now not be visible in the sprint on the planning board anymore.
4. Delete the sprint using the "x" button.
Result: Error: This issue cannot be edited because of its workflow status.
Expected: When closing the issue, it is removed from the planned (unstarted) sprint, so the sprint can be deleted without errors.