Take a read....we need more solemnity. We need more priests to understand that the priesthood includes the deaconate and the acolyte (subdeaconate). They were ordained/installed for both. They have a right to function in those roles regardless of their current stature, as priest. They are fulfilling their ministry in any action by which they were installed or ordained.
Notice in the article that the good father does take the time to say his own Mass, so he is not somehow "shirking" his responsiblities as a priest.
A Priest's First Time out as a Deacon for the Solemn TLM
God Bless this holy priest...