I have on several occasions completed a VDP merge between a master-booklet (saddle) and a similar addressbook file with records.

1st set When I get the final merged file it put the address on 'correct' (page 12 of a booket) page.
2nd set address suddenly appears on page 6.
3rd set address appears on page 12 (correct placement)
4th set address appears on page 6 (wrong)
and so forth ... so every 2nd set has wrong impose ...

i've tried to set the 'define record lenght' but if I do that i'm not able to use create/use master...

instead when setting up my address document i do the following:
a) import 600page into hold
b) rightclick, impose, saddle and save&close (in this step I can visually see the wrong placement)
c) properties on job, go to vdp, use master 1, enable enhanced freeform, define mapping, define 6 page master, 6 page variable file, map correct pages.
d) process hold
e) files are now merged BUT addresses appear on wrong page every other record.

hope that someone perhaps can shed some light on this...