It's not uncommon for balsa to bow, although there's factors that can either prevent it or amplify it. Our goal is to prevent it though. That's why it's suggested to weight balsa down flat when laminating, that's about the only guarantee we have for the flattest outcome possible. The only way balsa will warp later down the road is by being exposed to moisture or elements/climates that are extreme. Don't leave your model in a damp garage, and don't leave it in a 140 degree garage or car for any length of time... and when you're out for a day of flying, keep it in the shade or covered in some way. Of course that makes sense though right. If your skin is hot/cold/wet/moist your model is too... LOL. So keep your models and your pets comfy... and neither one will bow or warp.
I've laminated parts very similar to what's described here. I've used slow cure epoxy, rolled on with a weenie roller from the local paint department, then set the assembly on the flattest table I have and stack several 12"x12" pavers on the whole thing, then forget about it for a day. The components come out very straight, and very solid/stiff.. and have lasted many years.