The topic mentioned by Deano92964 'should' solve your issue. The original code fails because the function defaults the $bRememberMe to false whenever the function is called.
In the case of my patch, it checks to see if the form post variable is set and if so, changes the $bRememberMe to true thereby allowing the rest of the boonex login function to react properly and create the cookie.
I am currently running it on my site and my members say it works -- tested on Windows2003 Server R2/IIS6 and it works -- can't speak for linux, but there is no real reason it shouldn't -- it's a generic php hack :)
Let me know if it works for you -- maybe I can get it submitted to Trac for next version for everyone.