As identified in this USU support-thread post, the page= parameter is no longer considered an exclusion.

Using a fresh zc157a (beta) install with the demo products, specifically the Test Examples category, click on the categories sidebox to view the first page.

zc155f: <link rel="canonical" href="http://localhost/zc155fusu/index.php?main_page=index&amp;cPath=23">
zc156c: <link rel="canonical" href="http://localhost/zc156posm/index.php?main_page=index&amp;cPath=23" />
zc157a: <link rel="canonical" href="http://localhost/zc157a/index.php?main_page=index&amp;cPath=23">

Now, click to navigate to page 2:

zc155f: <link rel="canonical" href="http://localhost/zc155fusu/index.php?main_page=index&amp;cPath=23">
zc156c: <link rel="canonical" href="http://localhost/zc156posm/index.php?main_page=index&amp;cPath=23&amp;page=2" />
zc157a: <link rel="canonical" href="http://localhost/zc157a/index.php?main_page=index&amp;cPath=23&amp;page=2">

Not sure when in the zc156 releases this unwanted change was introduced.