We're having similar issues putting our PPML capacity to effective use.
We've got Gutters showing up in the Impose GUI wherever we set them, but never on the output media when printing.
We also have problems printing 2-UP, 3-UP, 4-UP or MORE-UP projects. We'd set our Bleeds and Gutters and they'd look fine onscreen in Impose, but when we hit the "green button"- Crop Marks, Bleeds, Gutters etc. print wherever they feel like.
It used to be that we could Impose and Print via PPML on one of our C7000VPs (A3100- we got them a year apart) - on the latter acquired and moreso "updated" of the two, then transfer the Imposed file over to the other (A3000-the former acquired machine) and everything would run smoothly.
So, a natural solution seemed to present itself: if we updated the software of the former A3000 to match the latter, the problem would be solved...
However, since we've gotten the former (A3000) updated to match the latter (A3100) ... both now have the problem.
Apparently, Canon has quite a number of open tickets with this problem as the focal point...they just seem to be dragging their feet on the issue.