  The fascination with the blazar OJ 287 stems not only from its status as a
prominent candidate for a close supermassive black hole (SMBH) binary, but also
because of the thermal bremsstrahlung origin proposed for its giant optical
outbursts. These outbursts arrive as pairs, quasi-periodically every $\sim 12$
years, based on the unique 130-year-long, well-sampled optical light curve
available for this blazar. For its three well-known, large quasi-periodic
optical outbursts (QPOOs), observed in 1983, 2007 and 2015, optical
photo-polarimetric monitoring has been reported in the literature. For these
initially radio-undetected QPOOs, widely acclaimed as `bremsstrahlung flares',
we have scrutinised the available measurements of optical polarisation and
spectral index during the rising phase. Several inconsistencies of these data
with the optical bremsstrahlung interpretation are noted, which point towards a
synchrotron-dominated alternative interpretation for all these prominent QPOOs,
just as for the optical emission observed between the outbursts. Possible
reasons for the radio non-detection of the QPOOs during the initial stage are
outlined.
