i also had this problem with mine, i still dont know why it did it. i had to switch it back to the standard setup

dear all, i have some problems with my brake, i need some advice from u guys. i had done the s13 caliper and disc conversion, but when i done my bleeding process, my brake still feel like no pressure, when i press the pedal, no pressure at all. i had done few times bleeding and still the same. i notice when i pump my brake pedal the brake fluid level in tank will decrease and after i release the pedal it will increase again. what really happen? is my mastercylinder faulty? i'm still using original master cylinder with servo from B310. please help. Thanks.