1.12 I am unable to set an anvil's repair cost window property. The API method returns true, but the value is never sent to the client.

@EventHandler
public void onPrepareAnvil(PrepareAnvilEvent event) {
    boolean result = event.getView().setProperty(InventoryView.Property.REPAIR_COST, 50);
    System.out.print("Result: " + result);
}

This worked beautifully in 1.11.2, and I've checked the server implementation against the wiki.vg protocol and nothing seems to have changed there.