I think this was happening to me too. But my situation is a little different cause I'm making changes as you know, so I haven't payed much attention to that, because It's another product type, and didn't know what was doing what.

I actually posted my doubts in bookx thread in #post1304799

But then for some reason things start working, but I read this and looking now at some exports files all I got 0000 too. So I didn't quite understood if this was happening on admin product insert, or in the imports / exports.

As I said, just saying that I've seen this, but it's not very relevant has I'm messing around with ep4 ad database a lot, and haven't tested only this field.