I've always bad luck (charring) with real aircraft plywood. I don't know that much about the "hobby plywood" you are using but it's all about the glue. I've had very good luck with some local 3ply ~1/8" birch plywood I've been getting.
BTW, what kind of models do you work on? Obviously some Bud Nosen stuff but do you work on other? I do a little model stuff. Here's a link (http://www.rcgroups.com/forums/member.php?u=26240
) to some of my stuff.
2.x laser ( Mach3 | SmoothStepper)| FSE 40W laser (RetinaEngrave) | DIY CNC Router (EMC2) | Rhino v4