I don't know how often this happens, but I lost with quads today. In fact, I was only ahead pre-flop with pocket 3's and I was still only 49% to win. Villian flopped a str8 which was also str8 flush draw open ended. I flopped bottom set. Turn gives me quads and him a str8 flush. Fortunately it was only a 58bb pot, but yikes! I thought quads ALWAYS wins.