Some report filters cannot be set by URL parameter; when these filters have default values, this can cause surprising changes in report output. This looks like a bug, but I'm not sure the best way to approach a fix.
The report "Donor Report (Detail)" by default shows donations with "completed" status, and for each donation the country value is a clickable drill-down link that filters the report by that country. So you can click on "United States" and filter the report to show only donations from US contacts.
But when you click that link, the status="completed" filter is not passed on, so the drill-down report shows donations from US contacts, with ANY status. That's not so bad, if you're watching the QILL criteria carefully, but now it gets stranger:
If you now click a button that reloads the report -- say, the "Preview Report" button in criteria, or the "Go" button on the pager -- without modifying the criteria at all, the report will apply both filters: country="US" and status="Completed". So, although you didn't change the criteria, the criteria have changed, and so the report numbers have changed, too.
What's going on here? There are a couple of oddities:
1. When the drill-down link is clicked, the default status="completed" filter appears to be set in the Report Criteria section, but it's not actually affectign the report output.
2. The drill-down link doesn't pass along the status="completed" filter; I'm not sure if it should, but if it did, we would expect it to fix the problem.
3. Stranger still, even if it did pass that filter in as a URL parameter, the report wouldn't apply it. From looking at CRM/Report/Utils/Get.php, it looks to me as if report filters must explicitly be defined with a 'type' value (one of CRM_Utils_Type::T_INT, CRM_Utils_Type::T_MONEY, CRM_Utils_Type::T_STRING, CRM_Utils_Type::T_DATE, CRM_Utils_Type::T_DATE, or CRM_Utils_Type::T_TIME) -- and if they're not, they cannot be set with URL parameters.
So right now, it happens that the applied filters change just by advancing the report pager. But I'm not sure what solution to suggest. Any thoughts?