I can't give a definite answer here, but I've never heard nor experienced anything like this. Could just be fear mongering and nintendo paying people. I've used my powersave ~300 times or so if i had to guess, and no problems here
Does anyone know of this actually personally happening from someone using these power saves?
Not here.. for me its like a 1/100 chance of getting a corrupt save, and thats why i keep automatic backups on so i can just restore the save and try again.
Nothing is wrong with the items.. its just 4bytes of data, nothing too complex. As for the pokemon, theres gonna be some things that are off that will show its not legit, but nothing bad will happen from owning it..
I've used my PS hundreds of times, let my maxed out pokemiles update to PGL, battled with diancie and M-lati@s in a street battle, and a bunch of other stuff.. Nothing has happened yet.