Steps to reproduce:

1. Find a widget with pagination, e.g. custom vars report - http://demo.piwik.org/index.php?module=CoreHome&action=index&idSite=7&period=day&date=yesterday#?module=CustomVariables&action=menuGetCustomVariables&idSite=7&period=day&date=yesterday
2. select "all" from dropdown where you can select how many items you want to see
3. click next few times

result: you can navigate through unlimited number of pages

see "-4 -- 6 of 1"