I had that. It turned out to be caliper pistons dirty, hanging up on their rubber seals, which tended to pull them back in too far when the brakes are released. This effectively disables the auto-adjust capability of hydraulic brakes. The fix is in the self-help area, which will tell you how to remove the caliper(s), pump the brakes out on some kind of limiter, like a trowel or some such, and clean the caliper brake pistons. I believe you press them back in, and repeat a couple of times, then re-bleed, since there could be a bubble resting in the top of the caliper, that gets dislodged when you push the pistons back in, and heads up teh line a bit, where you can get it by bleeding.
I re-bled several times. No change. Rebuilt the master cylinder...only a slight improvement. Had the caliper pistons cleaned, and it has been good ever since.
Don't go by this. Instead, find the real self-help thread and use that. I'm probably missing something.
Enjoy,
Rich P