Apparently, this is a big deal on the internet, causing many people to speculate about parallel universes converging. Lots of people (including myself) remember it with an E, while if you buy a book now, it will have an A.
It was Berenstein and the misconception has NOTHING to do with parralell universes it has to do with the fact that when people are little kids they often mispronounce and think things are spelled differently
People just need to stop with this nonsense. It is an A and it has always been an A. You "remember it" with an E because sometime in the past you incorrectly assumed it being written with an "E" because that is the most common spelling of stein so the wrong information got fixated into your memory. You just have been wrong the whole time, is there is all to it.