The Celebration stamp issued today in self-adhesive panes of 6 has TWO different die cut varieties.
The 3 stamps from the left hand column start (and end) with a "valley".
The 3 stamps from the right hand column start (and end) with a "peak".

(At least) twice before this has happened (two different die cuttings from the same booklet): 2005 Christmas issue (Snowman) and 2008 Lifesaving Society Centennial.