Merton thought that the idea that Bulgakov claimed Sophia as a fourth hypostasis, was a mis-reading of Bulgakov. In any event, Merton himself never saw Sophia as a fourth Person of the Trinity.
Bulgakov and Sophianism were denounced by the Church, any way you slice it. Whether Merton misread Bulgakov is, therefore, a moot point.
It should also be noted that sophianism was not invented by Bulgakov. The "icons" of Christ Holy Wisdom (where Christ is painted as an androgynous or feminine winged youth sitting on a throne) began appearing in Russia the 16th century. A decree of the Holy Synod of the Russian Church proclaimed on May 21, 1722, prohibited a whole series of icons which were deemed to be “contrary to nature, to history, and to truth itself”.
Included in this list was “…the image of the Wisdom of God in the form of a young girl…”
So the sophianist problem and its condemnation are nothing new. Yet, the wayward wheel kept being reinvented.
More recent decrees, such as those issued by the Moscow Patriarchate in May, 1935, and by the Synod of the Russian Orthodox Church Abroad in October of the same year, also forbade such portrayals. These decrees were issued in response to the growing popularity of the Sophian heresies promoted by Soloviev, Florensky and Bulgakov.
And still this heretical "theology" keeps popping up .....