Repairing armour with 4 enchantments becomes ridiculously too expensive even if renamed

Example : Diamond Helmet Prot.4, Resp. 3, Unbreak. 3, Aqua Affinity 1, renamed :
Originally costs around 12 levels (Can't remember exactly, but it was less than 15). After first repair with diamond, 24 levels to repair. And then the next time, it says too expensive. I go in creative mode to see how expensive it has become, and it is 192 levels! Even though I renamed it, and even if I had not, it should only have increased by 2 levels.