I admit that this is a shot in the dark...
Once I accidentally* overfilled my master cylinder and the brakes acted up; not fun. There needs to be room for the fluid to return to the reservoir. After removing some fluid, the brakes worked normally. I wonder if your remote reservoirs are causing the problem? You could try removing the top of the m/c (thereby taking the remote reservoir out of the equation) and see if it makes a difference.
* I'm using a better light when checking/topping up the master cylinder now.
