Shows the importance for height checks, distance verses height. Not just for the NPA's but as a cross check to the trusty ILS.
I have seen a few strange captures in my time, luckily I was always awake enough to catch it and takeover manually.
One springs to mind in Canada when the signal was being affected by a snow bank (I think) anyway after capture it caused the GS signal to fluctuate up and down... And of course the autopilot followed it, so it was click click and back to manual!