Have multi variation listings changed?

[teap0t42]

I'm going through my listings editing a few things, and I noticed on all listings which aren't already multi-variation that I'm getting a message saying they can't be upgraded to be multi-variation.

Have the criteria changed for what can be an MVL, as in the past I have altered several from a single to multiple items. Indeed, the only issue I had was when I wanted to change a listing back from MVL to single item I kept getting errors.

[padanpcparts]

It has to be a multi-variation from the start. once it is saved as a standard listing, you can not then select multi variation. 

[teap0t42]

Has that changed again? I've definitely changed listings to MVL in the past, but not in the last few years.