I get the same thing- it's coming from the threads or the connection of the tube to the bleeder. Some times I get a perfect seal and see no bubbles. Either way you're still pulling fluid out of the caliper, you just don't get that nice visual of "if there're no bubbles, then I must be done bleeding". As long as you've positioned the bleeder to be the highest point in the caliper, you should be good.
dave
