Sometimes that is caused by air being released. If you work in a garage and the day heats up, squeezing the wood fibers, air can get released. Often many instruction manuals tell builders to heat a room then gradually drop the heat as you glass.

It a tough call as far as a fix. You could just live with it or see if you can puncture the bubbles with a nail and float some epoxy on it. Sometimes there's no real acedemic solution other than some experimentation. Just be careful you don't make more of a mess than its worth.