Note: Please read
How to Report a Bug to understand what information is useful and the appropriate process.
For PHP 5.3/SVN
PHP-FPM now has it's own category in the official PHP bug tracker. Be sure to read "How to Report a Bug" above before submitting a bug.
Click here to report a bug - under "Package affected:" it is under the category "Web Server problem > FPM Related"
Old-style - The Patch - Stable (PHP 5.2.x and earlier)
Use the same suggestions from "How to Report a Bug" above. The PHP team does not support the patch, so you will have to work with the mailing list or possibly IRC.
Launchpad - 0.6.x Series - Some known issues (PHP 5.3.x and some recent PHP 5.2.x releases)
This version is no longer supported. Use the official SVN version now.
There is a bug tracker on Launchpad, but it does not get much attention. Try working with the mailing list instead.
Here is the link, in case you are interested.