The only way to achieve pure 100% stability (AFAIK) is cloning...same plant, same dominant traits.
And cloning is only for the photo world.
From seed, it's my understanding that even if a strain exhibits 3 or 4 phenotypes (auto or photo)
that it's considered stable or "locked in"
I think that's just the way the cookie crumbles when it comes to hybrids and crosses. They can't
lock it down to only one pheno type ALWAYS exhibiting (from seed).
So "stable" is a subjective term as it relates to expectation.
I think it would be incorrect to consider any strain "unstable" simply because it exhibits two or
more differing phenotypes. Auto or photo.
For what it's worth though, I've been hearing about herm and pheno issues with the Fast&Vast
line from Heavyweight.
I've also found that leaf shape changes as a plant gets older...I've had plants that the first few
sets of fan leaves were EXTREMELY Indica...short, fat fingers...that changed into Sati-thin leaves
as it got older and taller. So leaf shape and plant height are sometimes independent in hybrids.
The stability of a strain is more dependent on the breeding work/diligence and pheno selection
than it is dependent on whether it's auto or not.
For what it's worth, I don't think that Amnesia looks particularly Indi-dom...looks more 50/50
to me at this point.
My 2 cents.