Seroundtable.com problem to know its PR.

[hitech]

At the following page, it show zero PR, means no PR.
forums.seroundtable.com/index.php

But at forums.seroundtable.com, it shows PR 5.

It happen in many forums that the PR change by editing the forum address but same forum home page is shown with both addresses.

What is problem? What is the original rule of thumb to know the PR of forum?

[robinjackman]

That means google not crawl index.php page.