I have a flight booked (via Corporate TA) where outbound is GLA-Dubai-Bangalore with Emirates, and the return is Bangalore-Heathrow-Glasgow with BA. Looking at the return BA flights there is award availability to upgrade the Bangalore-Heathrow flight, however after a lengthy period on hold to the BAEC, they told me they were unable to process this as the sectors were 'married' and the TA needed to unlink them in order for BA to apply an upgrade using Avios. Is that common where there are mixed carriers on the booking? About to call the TA to ask them but just curious if this is actually the case or i should try calling again.