Unable to edit an issue when the user is deactivated

Summary

Attempting to edit an issue for a disabled user is not possible as it displays the following errors:

• If they're the assignee: User cannot be assigned issues.
• If they're the reporter: The reporter specified is not a user.

Steps to Reproduce

1. Create a user.
2. Create an issue and assign that user to it, and make them the reporter.
3. Deactivate that user.
4. Attempt to edit the issue.

Expected Results

The issue is able to be saved.

Actual Results

When saving the issue, the errors in the attached screenshot are presented and the issue cannot be saved.

Workaround

This validation is not applied when using Inline Edit, so it's still possible to edit those fields in the issue.
Alternatively the user could be renamed to lower-case, however, this doesn't seem to work in all cases.

Notes

This happens for users in the JIRA Internal and Active Directory.