As you can see, my graph consists only of a single swimlane node. All further nodes are within the swimlane. Nevertheless, the overview and print preview are showing that there is a lot of unused space in the upper left corner.
Consequently the graph is squeezed in the lower right corner on the print out.
yEd is obviously thinking that there is some content in the top-left corner.
Copying the swimlane to a new file doesn't work. Therefore I conclude, the problem is located within the swimlane thing.
I will not hesitate to follow any recommondations... ;-)
A screenshot of the problem:
These are the properties of the swimlane thing: