If you create a filter that includes a specific user or specific reporter, then create a two-dimensional portlet based upon that filter, the drill-down results will be incorrect when you reach IssueNavigator.

The problem is in UserParameter. Specifically, when you call SearchRequest.getQueryString() in the velocity template, if you have specified a user or reporter by name in your filter then UserParameter.getQueryString will be called and will return &assigneeSelect=<username> or &reporterSelect=<username>, instead of &assigneeSelect=specificuser&assignee=<username> or &reporterSelect=specificuser&reporter=<username>. This causes the assignee/reporter to be ignored, so you will get too many results when you drill down on the portlet.