[lbschenkel]

Exactly. The traditional design language is that an arrow besides a button indicates that the button will show a drop-down when pressed (traditionally without a line separating the two), or that clicking on the button will do the default action while clicking on the arrow will show all the actions (traditionally with a thin line separating the two).

Reusing that design language but making the button and the arrow two completely different buttons with their own actions sets wrong expectations for no good reason.