You probably already know this, so sorry if I am telling anyone how to suck eggs here.
With thin pieces to be planed, and in your case because there are lots of narrow sections of wood between cut outs, you shouldn't put the wood directly into the planer. Instead it should be mounted with double sided carpet tape, onto a board that is longer than the work-piece. This will prevent twist, chances of breaking the trailing edge will be diminished, and snipe at the end of the work-piece should be eliminated.
It took me a couple of years to discover this trick.