i was not trying to turn it into an arguing match but it is best you know more about the software before you go blaming it for not doing something. mysql is a database and that's it. they do not produce php modules or care anything about what php developers are doing to have php interact with mysql. it is php that has the modules built for interacting with various other software such as mysql, etc.
since mysql is all about mysql that is why you do not find anything in their docs about php. it is also why php leads the name of the package and not mysql.
i was a developer for a linux distro for the past year so i know how frustrating it is to get blamed for something that is not your responsibility.
actually come to think of it this error is not even really a problem mysql or php developers should have in their docs. it should be covered in phpBB's FAQs/docs since it is their software that is throwing you the error (note it could very well be in their docs/FAQs but i have not checked...did you?)