If your Squid version is more than a few months old, you should probably update it before reporting any bugs. Chances are that others noticed the same bug, and it may already be fixed.
If you discover a legitimate bug in Squid, please enter it into the Squid bug tracking database: http://www.squid-cache.org/bugs/. This is currently a "bugzilla" database, which requires you to create an account. You will receive updates as the bug is processed by Squid developers.
If you are new at reporting bugs, please take the time to read "How to Report Bugs Effectively," by Simon Tatham (http://www.chiark.greenend.org.uk/~sgtatham/bugs.html).
When reporting a bug, be sure to include the following information:
Squid version number. If the bug happens with more than one version, include the other versions as well.
Your operating system name and version.
Whether the bug happens every time or occasionally.
A good description of exactly what happens. Phrases such as "it doesn't work," and "the request fails" are essentially useless to bug fixers. Be very specific.
A stack trace in the case of an assertion, bus error, or segmentation violation.
Remember that Squid developers are generally unpaid volunteers, so be patient. Critical bugs have more priority over minor annoyances.