What we call 'curling' or as you describe it, the free edge coming loose from the overlay IS a very common phenominon for several reasons.
Imagin, when you apply L&P or any other system for that metter, to a plastic tip, the two become one because they are both plastic -- no chipping, no curling -- both the same density and they are inseparable.
When you apply most products to the natural nail, you have two different surfaces and two different densities. One - the natural nail is porous and flexible. Two - the acrylic overlay is less porous and less flexible SO when any trauma occurs to the overlayed nail, the natural nail 'gives way' and tends to split from the overlay.
The other problem is the nail plate being porous. It is continually soaking up moisture and then drying out - soaking up and drying out - this in itself tends to break down the adhesive where the nail tip was glued on and can lead to the natural nail 'curling' under the tip.
A few tips for maintaining natural nail overlays -
always extend the natural nail overlay just past the free edge so that it affords some protection to the plate underneath and
always during the rebalance, make sure you wrap the product around the edges of the sides of the free edge, so that it catches the natural nail and stops it from curling. And remember not to file away everything youve done when you are finishing the nail to a shine. It is really because the edges of the free edge (if you see what I mean) are not coated that this problem tends to happen.