Copper doesn't age anymore after cleaning once with axe

UPDATE: one of the blocks aged after a long time, so I guess it was just much longer, than the first time around. Please close this bug report! Thank you! 

Copper blocks aged without problem, but after I cleaned them with an axe, none of them continued to age. They behave like if they had been waxed, but I did not wax them.

I tried it with full blocks and slabs too, all of them "froze in their states of aging" after cleaning with the axe once. I cleaned them to different states of oxidization, and all of them seem to stopped oxidizing.