If you don't go to Select Subset, the pose will include the settings of all head morphs: Morphology morphs & Expression morphs. If you want to make a pure Expression pose you can apply to any character of the same type, you have to remove the non-expression morphs in the Select Subset window (otherwise, you'll lose your character morphology settings). If you want to save a pure morphology pose, remove the expression morphs from the list.