Nigel,
you could select idle thrust in one engine while the other was above idle in a Boeing Aircraft, but what you would never see is one engine trying to maintain Vapp after touchdown.
However, in all Boeings larger than the 737, The autothrottle remains engaged up to touchdown, therefore, the Throttles are moved to idle at about 27Ft RA. The B737 has a recomendation to disconect the A/T when manually flying the approach.
Regards