I was screwing around with a sorc yesterday, trying to use energy shield combined with damage to mana items. I socketed a cow king helm with an ith rune, to increase it to 50% damage goes to mana. After I was done messing around around I tried to unsocket it using the cube recipe. The recipe worked at removing the ith rune, but the item also lost it's 35% damage goes to mana trait.
Not sure if this is something new to 1.13 or if this is an already documented bug. I figured I would mention it either way.