This happens only on Openshift's MySQL - not locally.

On the MySQL doc I found:

For example, to use 4-byte UTF-8 character sets with Connector/J, configure the MySQL server with character_set_server=utf8mb4, and leave characterEncoding out of the Connector/J connection string. Connector/J will then autodetect the UTF-8 setting.

According to http://dev.mysql.com/doc/refman/5.5/en/server-system-variables.html#sysvar_character_set_server the server needs to be initialized with this setting