I am refinishing a table top. The top was distressed so I sanded it with a belt sander and removed all the old finish and distress marks and got down to clean wood. I applied a Minwax stain to the top and let it dry for just under 24 hours. It felt dry to the touch. When I applied the first coat of polyurethane color separated from the stain and mixed with the polyurethane and in many places formed dark colored bubbles. The end of my brush was actually colored with the stain color. When I used 220 sand paper to lightly sand the polyurethane it went down to the wood in places. I realize I will probably need to re-sand the top and then refinish it. Has this happened to anyone else and if so how do you avoid it?