DNS lookups only sometimes

I have an email validation script written in PHP that works on most Apache machines I try it on, with the exception (of course) of my production box that it needs to go on. This production machine is a Slackware 10.2 box, running Apache 1.33 and PHP 4.4.0. The script works if I call it from the command line with "php -f filename" however, if I try to call the same script from a browser (served by httpd) the DNS check is never made, and the script returns that the domain of the email address is invalid. The httpd people tell me that once Apache calls a .php page, PHP handles the actual parsing of that page, so if these DNS queries aren't happening when the page is called through a browser, what is changing from when they are called from the command line? Thoughts? Best, Jadel