OK465;
Interesting. I flew the -500 - shorter fuselage, same engines. I found it thumped less than either the A333 or A343. Those could produce a very benign settling or a real positive thump that bordered on 'hard' depending on how fast the tilt mechanism unloaded the bogies.
I don't have a theory either. The arrangement of the hydraulic manifold that services the brakes is one single unit which, while the four individual ports serve different brakes on the left & right bogie respectively, there does not a appear to be condition in which normal pressure would not be available to all brakes, and of course that is as it ought to be. So this may lend credence to the notion that it is a braking-system logic matter or a park-brake matter. Pure conjecture, though.
clark y, re "residual brake pressure", no, the BSCU, (Brake Steering Control Unit) does a residual pressure check and sends an ECAM message indicating "RESIDUAL BRAKE PRESSURE". I believe from the descriptions in the AMM that when/if the park brake is set to "OFF", pressure is bled off via the return lines.