Invalid "diagram name cannot be empty" (#1715)

When I insert a diagram the "add diagram" dialog propose a name for the selected diagram. But then a notification icon and msg "diagram name cannot be empty" is shown. And when I click Ok the new diagram is added with the proposed name without an error.

Btw the name contains a number which is automatically increased. But when I select a diagram, cancel my choice and try to add the diagam again the proposed name is "diagram2". Why?