The connectors have extra logic in them that processes the 5.5.5- prefixed version strings sent by MariaDB 10.0 servers. This logic expects that it is followed by another version string.
MaxScale 1.4.0 uses the string 5.5.5-1.4.0-maxscale for the handshake version string. The connector expects a connection string in the form of 5.5.5-10.x.y but fails with an NumberFormatException when it connects to MaxScale.
The fix to this is to change the connection string from 5.5.5-<maxscale version> to 5.5.5-10.0.0-<maxscale version>.