What am I missing here?
Hard to tell because I don't know where the border came from and whether that is included in the 5 x 10 or outside of 5 x 10.
You show a printable area of 10.766. If the border has been added to that, it might be larger than .12 inches, or greater than 10.766
On the other hand, did you change anything in the page layout tab?
See screen snaps 112 should be no checks on left side as shown.
Just checking...
Fred
PS I just check the size again in the 4000. If Borderless is invoked, the printable area should have changed to 11 x 8.5
See screen snap.Show 10.997 Yours shows 10.766