Edit: Strange as it sounds, it seems to be working as it should be, despite this. So, please ignore my ticket, and remove it as it appears things are working correctly.

------------------- Ignore below -----------------------

As found in prosilver's "overall_header.html", the variable in the line:

<link href="

{T_STYLESHEET_LINK}" rel="stylesheet" type="text/css" media="screen, projection" />

Which results in a line like this:

<link href="./style.php?sid=45b7acfc24c5f86522ba50031d851016&id=6&lang=en" rel="stylesheet" type="text/css" media="screen, projection" />

It looks like the phpbb3 system gracefully handles the "&" HTML code for ampersands correctly between the "id" and "lang" URL parameters. However, it does not handle the "&" correctly between the "sid" and "id" URL parameters. What results is that a blank, and empty page is loaded, rather than the correct/modified CSS stylesheet. This is testable on a 3.0.0 (Gold) site (which I have a fresh install of one I am working with now), by simply changing the "&" to a simple "&" after the session ID variable and before the "id=". So, example links (from my site) would be:

http://phpbb3.darkhelm.org/style.php?sid=45b7acfc24c5f86522ba50031d851016&amp;id=6&amp;lang=en

vs

http://phpbb3.darkhelm.org/style.php?sid=45b7acfc24c5f86522ba50031d851016&id=6&amp;lang=en

Unfortunately, since this seems to be reliant on the Session ID being present in the URL to see the bug, it may be difficult to rely on those exact links, but it is able to be reliably tested on any 3.0.0 Gold site that has a {T_STYLESHEET_LINK}

in its template, taking the value from that variable, and making it into an absolute URL rather than relative.