Maulana who made salaah behind a shia imaam

Assalamo alaykum wa rahmatullahi wa barakatuh

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Here in Pakistan, there is an ‘Islamic political party’ .One of the leaders of the party is a Maulana. This Maulana often emphasizes unity between Sunnis and Shias, he refers to Shias as Muslims and says that the similarities between Shia and Sunni are more and differences are less.
He once even prayed salah behind a Shia imaam ,openly.
Due to his above mentioned statements,views and actions, has this Maulana become a murtad?