Exporting clips with layers

I'm adding a rotational offset to an animation clip, which I'm exporting as an FBX (2019) file.  A second layer using Additive blending is used to add the rotational offset.  If I have the rotational offset layer selected when I do the export, the exported animation has only the animation frames based on the layers keys from the additive layer (Rotation Offset).  To get the animation to work properly using both layers, the Base Layer has to be selected before I do the export.

I'm not sure if this is expected behaviour or not.

Thanks.