Actually, that is fully documented - when using tools, the client sends another packet with coords all set to -1. Same thing happens with lava buckets (resulting in the server placing the lava at [-1, 255, -1])
Rev 836 had problems parsing rightclicks, so the second rclk actually never made it to the server
Rev 836 had problems parsing rightclicks, so the second rclk actually never made it to the server