Mandana Mishra was a Purva Mimamsa philosopher who became an Advaitin after losing a debate to the Advaita philosopher Adi Shankaracharya. He's often identified with Sureshwaracharya, although that's disputed. Now one of Mandana Mishra's works is the Sphota Siddhi, which seeks to defend Sphotavada. For those who don't know, Sphotavada is a theory of language advocated by Bhatrihari and other grammarians which states that humans understand language by hearing a Sphota or burst of sound which conveys an entire word or even an entire sentence at once. This is in contrast to the Varnavada theory advocated by the Purva Mimamsa and Vedanta schools, according to which humans understand language by hearing the sounds of individual letters, and then those letters are combined by the mind into words and sentences.
In any case, here is how Mandana Mishra describes the purpose of his Sphota Siddhi:
In support of [the doctrine of Sphotavada] which has been challenged by certain uncharitable critics, a few arguments are being put forward according to tradition and my understanding.
My question is, why does Mandana Mishra defend Sphotavada? Both of his gurus supported Varnavada rather than Sphotavada. His first guru, the Purva Mimamsa philosopher Kumarila Bhatta, refutes Sphotavada in this chapter of his Shloka Vartika. And his second guru, the Advaita philosopher Adi Shankaracharya, refutes Sphotavada in this section of his Brahma Sutra Bhashya.
Was Mandana Mishra just an iconoclast who decided that Sphotavada was right despite what his gurus said? Or did he have a third guru who believed in Sphotavada?