As has been pointed out, the lack of GPS has always been a main contributory factor with these map shift incidents, and as BOAC has indicated the additional DME planned for Innsbruck will alleviate this aspect of the problem.
However, there are two other contributory factors that are also being addressed:
(i) An updated FMC programme is on order, because it has been discovered that, particularly where a hold is entered - prior - to an approach, which has itself got a hold programmed into the go-around, the poor old FMC has been using virtually all of its limited computing power to sort out that conundrum and it has therefore not been updating the position even when signals are available;
(ii)The current BA policy of a mandatory go-around in the event of a 'hard' warning, even when over the runway, has been reviewed - watch this space !!