MyBB Community Forums

Every time I add a new plugin to my forum, the settings.php url continues to reset the 'bburl' itself to an old link. I used to have it as, for an example, 'Google.com'. Now I have it as 'Google.com/forums' but, every time I add a new plugin, I have to go back into the settings.php to set the bburl back to 'Google.com/forums' from 'Google.com'.
Am I missing something?

basically settings.php file should be writable & bburl can be first set correct in the file
& next at the Site Details page of Configuration section in forum admin panel