I use my SP3 with the dock and have three external monitors connected. Two WQHD (2560x1440) connected with the hdmi dongle to the mini display port on the dock and the slate, I then also have a HD (1920x1080) connected through USB with a separate USB2HDMI adapter. This setup has worked without a hitch. Last night when I came home I decided to watch some video. For that I didn't need the HD screen so I didn't turn it on, nor did I turn on the USB hub the adapter is connected to. Instead I only turned on the two WQHD monitors and then the SP3. This time it only stated up one of those monitors, the one connected to the dock, and ignored the monitor connected directly to the slate. Why would it do something like that?