On a recent project (red oak) I noticed that then I tried to brush on a coat of polyurethane a decent amount of stain lifted out of the wood. The color of the piece changed quite a bit because of this. Is this because of bad stain? Or is it because of the finish not being sealed? Should I seal the stain with a spit coat of shellac first (As Scott Bryan mentions)? Would that prevent the smearing and stain transfer? Would I just brush on the shellac?