Redmine

When two users edit the same issue concurrently, and the user with the stale edit has added an attachment, the attachment is lost after conflict resolution.

Steps to reproduce
User A opens the edit page of an issue.
User B opens the edit page of the same issue.
User A uploads an attachment but does not save yet.
User B modifies one or more issue fields and saves successfully.
User A saves the issue.
Redmine shows the conflict resolution screen.
Choose any available resolution option and submit.

Expected behavior
The attachment uploaded by User A should still be attached to the issue after conflict resolution.

Actual behavior
The attachment uploaded by User A is lost. The conflict resolution UI offers no option that preserves it.