The reason for the change to +8m reading on landing is probably because of dodgy conversion logic between feet and meters.
Although the aircraft's systems know it's on the ground (via the squat switches), I suspect that the implied 0ft AGL altitude is being interpreted wrongly by the passenger display system as zero to the nearest 25ft (25ft being the resolution of the altitude encoding on most modern aircraft).
And 25ft happens to be 8m when rounded to the nearest meter.