You can certainly consider the synchronized logins a bug; that’s your choice. And you would be the first to think of it as anything but a great feature. Every bit of feedback I’ve received about the way BridgeDD handles synchronized logins has been extremely positive. In fact it’s where I’ve received the most compliments. It’s safe to say I will not be changing this part of BridgeDD at any time in the future.
Also understand that the vast majority of people using BridgeDD are disabling logins/registrations in WordPress since the process in phpBB is much more secure and has built-in anti-spambot support.
Having said the above, you have given me an idea for a BridgeDD feature enhancement. Right now phpBB has a minimum limit of one day on its persistent cookies. If I reduce that to one hour, BridgeDD could control login timeouts in WordPress to as little as one hour. That would eliminate the need for a login timeout plugin in WordPress.