Shape key assuming a deformation as soon as it's created!?

I have like over 20 shape keys that worked perfectly, now all of a sudden, when I add an additional shapekey, before I even name it anything, it somehow assumes its own deformation even though I didn’t edit any part of it yet! None of the other shape keys did this, but no matter how many times I delete and create a new shape key, it keeps somehow being created with this premade deformation.

Yeah, I’ve seen this too, and I don’t know why, but there is a simple workaround. Pin basis, choose “new shapekey from mix” from shapekey specials.