Closing the run-time preview window should not close the run-time editor

Current Situation

when closing the run-time preview window in the run-time editor with the x button in the upper right corner, the whole run-time editor will be closed.

Desired Behavior

It should not be possible to close the run-time preview window with the x button in the upper right corner. Instead of this only the close button will close the preview window. The x button should be removed from the preview window. This is the same behavior as e.g. in the "Add Frequency" view.