1. Add a custom field CF-A of type Version Picker
2. Create a version named "version1"
3. Create a filter that searches for issues with the value "version1" in CF-A. Add the column CF-A in the Issue Navigator. Run the filter and this should show no issues
4. Create an issue with the field CF-A set to "version1"
5. The filter now correctly shows the newly created issue
6. Now edit that issue and set the value of CF-A to "Unknown"
7. Click on Return to Search, or Find Issues to see the results of the search. Rerun it and refresh the results

The problem is that the issue still appears in the search result even though the value of CF-A is Unknown, as shown in the attached screen shot. After reindexing, the problem goes away, so I suspect that the change to the issue is not updating a cached version of the issue?