Not a limited feature, there's a bug biting you.

TL;DR

The GoZ feature isn't locked out for HD morphs. It was used to create the HD morph packs for LaFemme. But, yes there's a bug lurking in there someplace. I've had it blow up HD morphs. Save well save often and never overwrite the last save. Keep tormenting. The no-repeatability nature of subD is a design limitation of Pixar Sub Division. The sub divided mash is created on the fly and even the most minuscule change in the source geometry will change the winding order and/or vertex count in the SubD mesh. That's why there isn't a OBJ to HD mesh import. It just wouldn't work.

It's been my experience that If I do one morph at a time and save between each morph I can "usually" get through without issues. The problems seem to occur when you work with multiple morphs or repeat edit the same one. If you need to re-edit save and reload before reworking the morphs. And again always save the original in case it messes up and you don't notice it..