Can't add Matinee to Data Only Blueprint

I’ve got a data only blueprint with a UPROPERTY for an AMatineeActor*. When I try to add a Matinee instance from my map, the list shows a few I could add, but clicking on them just leaves the slot on the blueprint blank. It does “dirty” the blueprint, which makes the little compile cog have the orange ?, but nothing gets added. The same happens if I try to drag a matinee instance from the scene into that slot: the box lights up green like it could accept the instance, but when I drop it in, the slot remains empty but the blueprint is dirty again.

Am I missing some step, or is this a problem with matinees in blueprints?