Animation preview additional mesh curves not being driven

I am currently animating a metahuman character using an animation sequence that targets the body, this sequence includes all of the metahuman face joints and curves so when the body pose is copied in the metahuman face animation blueprint the face is being animated by this sequence as well.

The issue I am having is that since this animation sequence targets the body it is not possible to preview this animation on the face mesh. There is the option to add the face mesh to the body as an additional mesh when previewing, however this only animates the joints of the face and not the curves. After investigation this seems to be due to the fact that the additional mesh uses a default animation blueprint with a ‘Copy Pose From Mesh’ node without the ‘Copy Curves’ option enabled. Looking at the source code seems to verify this.

In the function FAnimationEditorPreviewScene::RefreshAdditionalMeshes there is an ‘if’ statement(line 384) that implies the intended ability to use custom animation blueprints for the additional meshes. However the check will always be false due to “AnimInstances[MeshIndex] != nullptr” being false, and therefore the default animation blueprint will be used instead which as stated does not drive curves. I tracked the issue to the function UPreviewMeshCollection::GetPreviewSkeletalMeshes which looks like it is supposed to retrieve an array of both the additional meshes and an array of what I’m assuming is meant to be user selected animation instances for these meshes. The problem is that the function seems to be half implemented as whilst it returns the meshes just fine, it always returns a nulled array of animation instances. If this feature were implemented that would allow me to set a specific animation blueprint to preview the face with and therefore ensure the curves are being animated, but this feature appears to be missing.