I was rewatching episodes of The Angry Video Game Nerd (yes, I'm hooked) and I came across his video on The Berestain Bears games. He stated in the video that he remembered it as being Berestein, and that's how I remember it as well. It seems as though evidence points it to always being Berenstain. I vividly recall it being Stein not Stain as a kid.
There are entire theories dedicated to The Berenstain Bears, and the Mandala Effect, along with other "false memories". Some people even seem to believe it points to alternate dimisions.
https://www.vice.com/en_us/article/the-berensteain-bears-conspiracy-theory-that-has-convinced-the-internet-there-are-parallel-universes
What do you remember it as? Do any of you have any theories? Or do you think a ton of people just have a shared false memory?