Question [SerializeField] InputActionAsset always null on editor startup

I've got a fun little wrapper class that has a serialized InputActionAsset field. Unfortunately, every time I start up the editor, whatever I've got saved in there is gone. It works fine in every other context, and appears in asset file correctly, but never actually persists. There's nothing else fancy going on. Just a simple serialized field.

I've poked around in the docs and searched the forums, but come up empty. Is there something I'm missing here?