When creating/editing a "Set Audio Level" action, selecting the "Application" option disables the "OK" button(as the field is blank by default), but typing(or pasting) into the dropdown does not re-enable it.
If the "Volume Setting" option is changed after this, E.G. from "Mute" to "Unmute", "OK" will be re-enabled(provided "Application" is not blank).
Actually using the dropdown to select an application from the list does enable "OK".
EDIT: Fixed in v1.7.2.26