UBB only supports up to mysql 5.5+
requirements
PHP 5.4 - 5.6
MySQL 5.5+ or MariaDB
Meaning mysql 5.6 has not been tested.
You may need to downgrade your test server.
I believe your math is broken for today :/
UBB.threads works just fine with MySQL 5.5 or higher. the plus symbol ( + ) means 5.5 is the lowest version. Anything equal to or above 5.5 is recommended.
For example, many sites, including my own, are currently on MySQL 5.6 without issues.
