How about some magnets to hold the rear panel in place?  Place the magnets in the cabinet and embed some thin washers just deep enough that they sit flush.  

Are you using a router to trim the veneer on the edges?  When trimming veneer on an edge I prefer to use a knife.  Anytime I have used a router, I get some sort of chipping or tear out.  They make special trimming knives for that but I just use a utility  or Exacto knife with a fresh blade.    

EDIT: I just reread how you trimmed the veneer with a knife and looked at the pictures more carefully.  It probably does not hurt to score it on the backside but I usually cut downward from the front side.  It might also help to have much less of an overhang on the edge when you trim it.  This allows the wood you are trimming to sort of curl away as you cut.  




--Nathan, TX. Hire the lazy man. He may not do as much work but that's because he will find a better way.