Possible that your tree has been taken over by suckers from the
rootstock? Trace those fruiting branches and see whether they come from
below the union. Dwarf pears are often grown on quince rootstock,
sometimes with an intergraft to improve compatibility; if the suckers
on one of these are allowed to grow enough to start bearing (neglect
them a few years, and they just might), they'll bear quince.
--
Chris Green