Legal Use of 20c Palace Official on Dues Notice

1927 LABUAN, BORNEO to MANILA
Postmarked LABUAN / 21 AP, transit JESSELTON on the same day.
Taxed 50 centimes as franking removed for unexplained reasons
(no sign of postmark on stamp remnants).
Partial MANILA entry on 20c Palace OFFICIAL for the 50c Dues.

This is a commercial cover. Without doubt the Bureau of Posts authorized
the use of the Palace OFFICIAL issues on non-government mail.