Can you contact Samsung? I'm in contact with Sabrina from Samsung Support on Twitter. I'm working with Samsung Support to get it resolved, but since my device is a developer device I'm not entitled to the same support level as a retail user would get. This seems like a driver/hardware issue with the dock. If I install the Windows 8 drivers from Intel, it behaves just the same. This is with the standard Windows 8 driver (1.2) from windows update. After that undocking and redocking brings up the external display again. It will keep working until the device goes to sleep. This will make windows detect the external display and allows you to extend to it as you normally would. Insert the tablet into the dock (thus while doubly connected).Extend the display while the tablet is out of the dock (this has always worked).

Connect the monitor to the tablet using the other cable.Connect the monitor to the dock using one cable.I can get it to work using the following funny workaround: This is while having the display connected using a HDMI->DVI-D cable or a HDMI->VGA cable.

When I insert the tablet in the dock, power it on and have an external display connected, nothing is shown on the external display. I have a strange issue with the HDMI connector on the dock.

Microsoft display dock hdmi problems