I guess this one is a common problem, but it took me a while to figure out: If you use WebDAV to author your site (as I am doing on an internal box), PHP will process all GET requests for .php files, sending the resulting output to your editor.
One way around this is to configure an Alias for your web site with the right php_flag to switch the engine off. Here is a boilerplate configuration that does that and a couple more things I like when I’m doing development (like asking for a password):
Alias /davshare /var/www/html
<Location /davshare>
php_flag engine off
Dav On
DAVMinTimeout 600
DAVDepthInfinity On
AllowOverride AuthConfig Indexes Limit FileInfo
Options +Indexes
IndexOptions FancyIndexing
AuthType Basic
Require valid-user
AuthName "DAV Editing"
AuthUserFile /var/www/etc/passwd
</Location>