Comment to Events Map
SOLVED. But a bit strange. Viewing the event. NOT editing. Simply adjust the location on the map in event-view. Gotcha.
Never thought, that this has to be handled NOT in the edit-event-page.
The event-edit page allows only to provide an address but not the exact location. Moreover it requires the google geolocation API to be enabled. While the map on the view page allows to precisely point the exact location of an event directly on a map by placing/dragging a marker, even if an address has not been provided at all or is not available for the event.