There will surely be the time where you find a bug in PHP, but prior submitting half hearted bug report make sure you've accomplished the following things:
- search the bug tracker if the bug has already been subbmitted
- put together a short and behaviour reproducing script
- verify the behaviour with the latest version AKA snap of PHP
- if PHP crashes, generate a backtrace
If you're in doubt, read this if you didn't already (which you shouldn't tell anyone by the way).