Formatting of YEAR values is controlled by the MySQL driver, and by default they are displayed as dates (for more information, please see https://dev.mysql.com/doc/connector-j/en/connector-j-YEAR.html). To change this, open your connection and choose "Driver Properties" in the Properties tab. Find the property called yearIsDateType and change its value to false. Apply the changes and reconnect.
You can also to it for all connections that use the same driver by doing the same adjustment for the corresponding user driver in Tools->Driver Manager.