Anvil leather pants bug

i expected the leather pants were going to be repaired:

i was going to repaire some cyan paintet leather pants when i took it out of the box and preesed 'the inventory button' it did not become repaired and i got the leather and the pants back but i did not got my 1 lvl back:

1. Put a pair of cyan pants in the anvil and then a piece of leather in the other space
2. then i taked the new repaired pants out
3. and then i pressed the 'inventory button' and then i got a piece of leather and the pants back but i did not get the lvl i used back