You have probably tried this already but rotate the block 180 degrees to make sure that a corner of the block is not resting on the ZIP socket lip. Also make sure that the water flow going into the Maze 3 is going in through the center bard and not on the outer barb.
Just stating the obvious possiblilities
One last idea... you mentioned that you radiator is in the top of your case and that you have your system setup pump->rad->wb->pump. Try switching the Maze3 round with the radtior so it goes like this pump->WB->Rad->pump I have a very similar setup where my radiator is at the top of my case and I have my system setup with the waterblock before the radiator and it works great for me. Couldnt hurt...
Some pics of you setup would probably help us with diagnosing your problems also
(if possible)