Client Hyper-V and Connected Standby
When you install the Hyper-V feature on a Windows 8 / 8.1 computer that uses the Always On/Always Connected (AOAC) power model, the InstantGo, formerly known as Connected Standby, power state is not available. This is noticed by developers install Visual Studio Express 2013 for Windows. Visual Studio will automatically install and the Hyper-V role, and Connected Standby will be disabled. Without Connected Standby the device will act more like a notebook and less like a tablet.
30 Jun 2014
Connected Standby is not available when the Hyper-V role is enabled
Microsoft KB article discussing this issue.
Surface Pro 3 Tip: Hyper-V vs. Connected Standby | Mobile devices content from Paul Thurrott's SuperSite for Windows
Article from blogger Paul Thurrott on Client Hyper-V and Connected Standby. Paul provides one work around.
Switch easily between VirtualBox and Hyper-V with a BCDEdit boot Entry in Windows 8.1 - Scott Hanselman
Scott describes a method of creating two separate boot entries one with Hyper-V enabled and one not. This is another potential solution to the issue.
TechNet topic on Client Hyper-V