I suspect you're right about the pressure cooker sandy. I've never used one, so mine is always the traditional pot on the stove job.
I always used to put the meat into the water when it was cold and bring it to the boil, but then I was doing some reading and also on a cooking show they said make sure the water is hot, so I tried it, and it was true. I don't know if it's just coincidence, or something else I do differently, but these days, we only have lovely, juicy, fall apart corned beef.