**Preconditions**

- Work package module activated.
- Backlogs module activated.
- Version exists.
- Work package A (e.g. Bug) exists that is assigned to a sprint.
- Work package B (Task) exists that is assigned to same sprint.
- Sprint is closed.

**Steps to reproduce**

1. Open work package B (Task) and open relation tab.
2. Assign work package A (e.g. Bug) as child to work package B and confirm.

**Actual behavior**

- Work package A can be selected.
- Error message “You must not write a read-only attribute” shown.

**Expected behavior**

- Work package A cannot be selected or more descriptive error message shown.

**Screenshot**

**QA system**

- demoproject.openproject.com
- OpenProject 7.3.1
- Chrome Begin of the insertion
End of the insertion