When my Surface Pro 2 resumes from sleep while in the Surface Dock, it does not put video out to the external monitor. Since I have it configured to only display on the external monitor when docked, I don't have any display. The keyboard wakes up, the USB hub in the monitor wakes up, and the monitor itself wakes up but then goes quickly back to sleep.
The only way to resolve it is to unplug the mini-displayport connector or re-dock the Surface. This is highly repeatable behavior. I have a Surface Pro 2 with a Surface Dock and a Dell U2913WM. I have the same setup at work with a Surface Pro (original) and don't experience the problem.