Mulit-DB Warnings

I have just installed Multi-DB on a multisite. I am receiving the following warning:

Warning: mysql_set_charset() expects parameter 2 to be resource, boolean given in /home/equine/public_html/wp-includes/wp-db.php on line 650

I know that I could turn it off in my php.ini but just want to check to make sure it isn’t something that could cause any issues in the future.

Thank You