Villagers will not become clerics

I have a savannah village (created using survival mode methods only - built an area, cured two zombie villagers, gave them workstations, bought a bell off of one to make a town centre, etc) where unemployed villagers won't become clerics (with brewing stands available close by with blaze powder in them).  The villagers are breeding to match the number of workstations but the ones that should become clerics don't (they just stay unemployed).  If I add other workstations they immediately take that profession instead.  The villagers are breeding to match the number of available workstations they just won't turn to clerics if any of the workstations are brewing stands.