SetDurability not updating client

I must be doing something wrong, because for some reason setting durability on an inventory item (specifically, the held item) does not actually post the change to the client until they right-click.

What I'm trying to do is prevent items from taking durability damage during mining. I update the value on the server and it works fine, but the client doesn't take the value. I've even tried pushing a Packet5 through to the player manually. Yet when the player right-clicks, something happens that forces the client to retrieve the new durability.

Any hints on what I'm doing wrong? Maybe I'm setting this thing in the wrong place? I've got it all inside the BLOCK_DAMAGE and BLOCK_BREAK events...