Custom post order when using OR relation

I have a custom post type named Faculty. Faculty must be one or more of the type: MCT, MLT, or MT.

MCT -> A, B
    MLT -> C, E
    MT  -> C, D

I want to list all MLT and MT faculty on a page in order by last name -> C, D, E

I am having a problem with the OR relation when used with orderby where it is returning all faculty that are MLT or MT or have a last name (which is everyone). The AND relation works correctly, returning just C.

My WP_Query arguments are:

Array(
        [post_type] => faculty
        [order] => ASC
        [orderby] => meta_value
        [meta_key] => faculty_last_name
        [meta_query] => Array(
                [relation] => OR
                [0] => Array(
                        [key] => faculty_MLT
                        [value] => MLT
                        [compare] => =
                    )
                [1] => Array(
                        [key] => faculty_MT
                        [value] => MT
                        [compare] => =
                    )
            )
    )

The SQL created is:

SELECT SQL_CALC_FOUND_ROWS wp_posts.ID FROM wp_posts INNER JOIN wp_postmeta
    ON wp_posts.ID = wp_postmeta.post_id INNER JOIN wp_postmeta AS mt1
    ON (wp_posts.ID = mt1.post_id)
    INNER JOIN wp_postmeta AS mt2 ON (wp_posts.ID = mt2.post_id)
    WHERE 1=1 AND wp_posts.post_type = 'faculty' AND (wp_posts.post_status = 'publish'
    OR wp_posts.post_status = 'private')
    AND (wp_postmeta.meta_key = 'faculty_last_name'
    -->OR (mt1.meta_key = 'faculty_MLT' AND CAST(mt1.meta_value AS CHAR) = 'MLT')
    OR (mt2.meta_key = 'faculty_MT' AND CAST(mt2.meta_value AS CHAR) = 'MT') )
    GROUP BY wp_posts.ID ORDER BY wp_postmeta.meta_value ASC LIMIT 0, 10

If I change the –>OR to AND, the query returns the correct result.

Is there some way to use orderby along with relation => OR in wp_query?