Labels don't stick on mining addresses

[Zannick]

Labels aren't persisting on addresses created with getnewminingaddress. You can set them in the qt UI, but they vanish after some time, likely on a restart.

Expected: Adding a label to any address saves it so I can see what transactions came in to that address without memorizing the address.

Actual: Some addresses don't seem to keep their labels. These are addresses starting with V, which are mining addresses. getaddressinfo reports they have purpose receive_miner.

Reproduction

1. Create addresses with getnewbasecoinaddress, getnewminingaddress. (and getnewaddress if you like, for stealth)
2. getaddressinfo <basecoinaddress>, getaddressinfo <miningaddress>. Note the labels field contains an element with name, and remember it.
3. In the GUI, change the label on the basecoin address.
4. getaddressinfo <basecoinaddress>. Note the name associated in the labels entry will have changed.
5. In the GUI, change the label on the mining address.
6. getaddressinfo <miningaddress>. Note the name in the labels entry has updated!
7. You can repeat this for stealth addresses as well. Note stealth addresses have a label field and a labels field; both update consistently when the label is changed.
8. Close the wallet and restart. The label on the mining address is unset.
9. getaddressinfo <miningaddress>. Note the name in the labels entry is empty again.

Machine info

Veil Core version v1.2.0.1-b108d57 (64-bit)
Win 10 x64