This is the hypothetical setup…
The page name is domain.com/poster/
It contains three P2 items named cats
dogs
horses
Fancy URL’s are set up, so the URLs to each item is…
domain.com/poster/cats
domain.com/poster/dogs
domain.com/poster/horses
So far, so good. When submitted to Google, it’ll see these “pages”.
But, P2 also does categories, so there are also the following URL’s…
domain.com/poster/?category=categoryname?post=cats
or something like that.
So now, Googles throws a wobbly because there are in effect two URL’s to the post called cats
The simple fix is to fire a canonical URL thingie into the header, but will that then tell Google to ignore all the P2 item URLs on the page as well as the one that includes the category name bit?
Tagging @Jannis on this, but also hoping others might be able to chime in with some expert understanding on this stuff. (Not insinuating Jannis isn’t expert!)