Thanks to a cookie hack Jon Gales found, I was able to figure out why Safari isn’t able to remain logged into PHP-Nuke based sites and I’ve made fixes to MacMegasite & WorldBeatPlanet.
It looks like Safari isn’t handling PHP’s setcookie() function properly. If no path is specified, it’s supposed to set the cookie for the current directory. Instead, Safari is using the name of the file it’s called from as the path, so it will only work within that particular page.
MacMerc has also applied the fix.