forms and php

I am fairly new to the php/mySQL combo and just noticed an unusual behavior and don't know where to find the answer to fix this. It is probably common knowledge, but not to a newbie. If I fill in the fields of a form and hit the "enter" key to submit the form, no variables seem to be passed along. If I use the submit button, everything works perfectly. It seems that other forms on the web work with the enter key just fine, so I am probably doing something to cause this yet I don't know what. I am hosted at hostgator.com and it has php version 4.4.4 and mySQL version 4.1.22-standard. Thanks, Mark Pashia