Actually in effect, the main verify_credentials function (even if it is very fast) retrieve each time the phpBB user's session, but what it do if users result to be already logged in wp, is just to check if email, password or url settings in phpBB have been updated, and update in WordPress in accord if required. It result to be not useful, if the phpBB WP extension has been installed into phpBB.
So that an option, that will switch the way the integration plugin will work if installed in conjunction with the phpBB WP extension in phpBB, will be added.
Moved to 2.6.7
P.s (not related plugin, but phpBB extension)
The NEW version of the phpBB WordPress phpBB extension is quite ready to be released.
It will not require to manually edit any config.php file, but only to setup into the ACP related settings page, configuring options.
The extension has been upgraded to be easier to be used for anyone.
Stay tuned! ASAP will be ready for the cool people