All the brakes have to be in contact with the drums/discs before ANY brake can produce a stopping effect. As long as any brake is still capable of moving, no pressure can build up anywhere in the system. That's particularly true of a single-line system, but even a dual brake system will have a spongy pedal until the slack in the master cylinder is taken up and the non-working chamber of the master cylinder is out of the equation. The laws of physics are not "suggestions". If a brake is adjusted tight enough to drag, the pull will be there all the time, regardless of whether the driver has applied the brakes or not.
A flex line that is restricted or collapsed on the inside can cause a pull because pressure can build up in the brake cylinder on the opposite side from the restricted line and cause only one brake to be applied.
Jerry
