Canon LBP7660Cdn Manual page 591

[Off],
[Alternative Method]
[On]
If this item is set to [On] and if the last page for the 2-sided printing is 1-sided
printing, 1-sided printing is applied to the last page. (Printing can be performed
faster than normal 2-sided printing.)
However, when performing 2-sided printing on punched paper or previously
printed paper, the orientation or printing surface of the last page may differ from
other pages. In this case, specify [Off].