In the Aerad supplement is says to ignore PAPI's below 200ft. If you fly into Heathrow, the PAPI's and glidslope do not match below 200ft on 09L, at least in the aircraft I fly.
As far as I remember without looking it up, the PAPI is not a required light for CAT1 approaches so in theory you don't need it for a CAT 1 approach to minimums. If you do pop out of the cloud to see the PAPI's saying something strange at 200ft, then the visual reference should be enough to land anyway - if its not surely a Go Around is the thing to do. They are good, but not perfect.