It's arguable whether or not cinnamon and black pastel are the same mutation of the same gene or different mutations of the same gene. I'm certainly no expert on either but from what I've read it sounds like there might be some subtle but consistent differences between cinnamon and black pastel indicating that they are different mutations even if of the same gene.

Same goes for lesser and butter. Some claim they are consistently different but others that if you mixed a group of the two together you couldn't tell them apart. Of course even if we can't tell them apart by looking there could be differences in the mutations of the common gene that might be important somewhere down the line (in supers or combos). Or butter and lesser could be the exact same mutation just imported two different times.

I know RDR had some trouble trying to cross I think it was lavender and albino with bad eggs but I heard someone else eventually did that cross and proved them incompatible with each other. So it could be that you are hearing about that case. If someone has actually crossed albino and caramel I would sure like to hear about it as there is a really old case that could be explained by them being alleles so it would be nice to finally know one way or the other.