The following seems not to be an important bug, but a little modification to PHP behaviour or some documentation on this could be useful:

If you use session_id("...") [ "..." means a normal SESSID] to force a special SESSID, session_start() will always(!) send the session cookie - even if the client sent the cookie with exactly this SESSID in the request.

Now the Problem:
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--> At least IE6 will hang endless (looks as if still loading the page) when receiving an identical session cookie the third time.

The normal way:
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session_start() - without using session_id(...) before - will send the session cookie only if it was not received from the client. This is the behaviour one would expect and which should be implemented for the case using session_id(...) too.

Of course there is a workaround available:

if (!$_REQUEST['SESSID'] == "...")
    session_id("...");
session_start();


--> At least a hint in the manual should be included since this may also cause others to lose some hours for debugging their sript, as me.