As far as I know this is normal behavior.
The outline you see in the 'NC Drill' is not the board outline, but some imaginary outline placed on the center of the outermost holes.
Try open it in a GerberViewer. I think you will see that everything is OK.
Thank you Klaus,
Next time I'll read the feedback from my supplier more carefully. The problem involved a via hole that was way off for some unknown reason. I re-made the NC File and it's now where it should be.