Good day!
I found a little mistake in version 3.0.1
I'm using Your premod beginning from the version 3.0.0 and i upgrade it up to 3.0.1. I made it in the following type: I uploaded the whole package on the site and made the script of the upgrade of Database.
The function of deleting SID is enabled. In many cases SID is deleted and it is not seen either to guests or to registered users of the site. Previously SID was always deleted automatically in hyperlinks, independent from the time of last visit.
But there appeared a strange thing after upgrading. If registered user visits the site in a few hours after last visit, then SID can be seen on the page in hyperlinks. Maybe there was a redirect with the code 301 or something else.
Users remembered during an hour (settings in Common Setup). User makes the note "To be remembered on the site" at visiting the site.
Maybe the problem is in variable header_sent.
Thank You. I hope on Your help.
You have a very good system.
p.s. I'm sorry for possible mistakes due to my bad english.

Have some idea:
on Apache worked gzip module. It compressed my php/htm/css/js output data. Maybe Apache send header (gziped) and SID not removed becouse header already sended (version 3.0.0 not test sended header or not).
In PHPBB gzip disabled, becouse used native Apache gzip module

It's normal if your user see SIDs when they just log in, as you said, these where previously redirected, but there is no need for this SEOwise, since bots do not log in, and they are redirected (so are guests) if they follow a link with SID.

See this as resources saving

I think it problem:
when registered users see SID's in URL's, users would send URL's in messages with SID's.
I think it bad for SEO, for beaty URL, for security.
May be problem in variable headers_sent in code:

if (!$this->seo_opt['zero_dupe']['on'] || headers_sent()) {
return;
}

I can not fix this, but I am confident that you will be able to do so

It not an SEO or a security threat, since SID are redirected for guest as well as when the SID sent does not match the one attended : http://phpbb3.phpbb-seo.net/?sid=829e0e ... 276fa5c095

Bots will never see SID while browsing your forum, besides, users are quite unlikely to use a link with SID since they won't see them really often.

++