bubbling in decals

Hey all. I've been having troubles with decals, nothing major though. When I put decals on the backside of windscreens, like on a Tamiya Kawasaki ZX-12R, Tamiya F40, and Tamiya Supra. When I put them on I press out all the bubbles. Everything is smooth, you can see that on the otherside of the window. But... as it dries little bubbles start to form. I try to press them out, put it won't work. Should I have used a solvent or a setting solution?