A workaround which I used up to now:
First reduce the graph size, then
click on the label to edit it, press Enter *), press delete
*)This time it doesn't closes the edit mode - but adds a newline.
Actually: it "adds" 2 Newlines - therefore one has to press delete to delete one of the two Newlines.
In the video it looks like going forth and back:
The "2ndLine" gets shifted out of the edit box & comes back.
To finish,
- click somewhere with the mouse to exit edit mode (... as pressing Enter would add another newline
- adjust the size of the graph and enjoy the magically added Newline.