Morph Targets in Unreal 4 aren't behaving


I’m doing facial rigging but I need a blendshape to correct some bad deforming in the eyelash.

It wasn’t working so I figured I’d isolate the problem by simplifying as much as possible:

A single sphere with a single joint and a single morph.

But when I import it into Unreal, I get a weird mess:

at +1

and at -1.

It not only goes off to the wrong side, but it also is twisting for some reason.

Anyone know what’s wrong and how to fix it?