I am using the latest version of Piwik available on the Synology DSM Package Manager.
When I am on the "Locations" page, viewing the "Countries" panel, if I select "All" from the drop-down, the "Next" button is still visible. If I click the "Next" button, the page number decrements. The image I have shows the list on page "-2" of "37" though there should be no pages at all.
I don't believe so, because it doesn't take the data away. It just shows negative page numbers with the same data. An aesthetic bug, not a function breaker.
This one should be meanwhile fixed. If not, feel free to create a new issue.