Currently, JIRA knows an issue is unresolved when the resolution field is not set. It determines, for example, if a link to the issue should have a strikethrough or not.

Also, the documentation states that a user shouldn't create an 'Unresolved' resolutions, because JIRA will not handle the issue as 'Unresolved' when using this resolution.

This approach has a very problematic characteristic: the resolution field is mandatory, but it not being set has a meaning! It is unresolved.

This brings a few problems:

• There is no flexibility. The users need to either use a post function and trigger a transition or change in the database in case they want to change a resolved issue to 'unresolved'
• We cannot add the 'resolution' field to the 'Edit' Screen for an issue type in a project. If that is done, the user must always set the resolution when editing the issue, even if they wanted to change a completely different field

My suggestion is to add a 'Unresolved' resolution, rather than understanding it as unresolved when this field is not set. It would have the following characteristics:

• This resolution cannot be deleted or modified
• This is a special resolution. When an issue has this resolution, JIRA considers it as unresolved (no strikethrough, etc.)
• You need permission to set as unresolved (otherwise, only the other options will appear)
• If the issue is set as unresolved, it can remain that way, no need to change it when editing an issue.

I think this resolves a question:
How can a required field give a meaning to an unset value?