Omit field is ignored if field type is marked useAttributeFor

@XStreamAlias("User")
class User {
String name;
String password;
}

xstream.useAttributeFor(String.class);
xstream.omitField(User.class, "password");

Upon serialization I get: (password should not be there!)
<User name="abc" password="pass"/>

However if userAttributeFor is not used I get (Correct password is ignored)
<User>
<name>abc</name>
</User>