Netstandard1.x Nuget packages cannot be installed for netstandard1.x projects

After doing a fresh Windows 10 installation along with latest Visual Studio 2015, netcore, and nuget tooling - I can no longer install Nuget packages to any .netstandard projects. Here's some example output:

Restoring packages for 'ClassLibrary1'.
Restoring packages for c:\users\zone1\documents\visual studio 2015\Projects\ClassLibrary1\ClassLibrary1\project.json...
Package System.ComponentModel.EventBasedAsync 4.0.11 is not compatible with netstandard1.3 (.NETStandard,Version=v1.3). Package System.ComponentModel.EventBasedAsync 4.0.11 supports:
  - monoandroid10 (MonoAndroid,Version=v1.0)
  - monotouch10 (MonoTouch,Version=v1.0)
  - net45 (.NETFramework,Version=v4.5)
  - netcore50 (.NETCore,Version=v5.0)
  - netstandard1.0 (.NETStandard,Version=v1.0)
  - netstandard1.3 (.NETStandard,Version=v1.3)
  - portable-net45+win8+wp8+wpa81 (.NETPortable,Version=v0.0,Profile=Profile259)
  - win8 (Windows,Version=v8.0)
  - wp8 (WindowsPhone,Version=v8.0)
  - wpa81 (WindowsPhoneApp,Version=v8.1)
  - xamarinios10 (Xamarin.iOS,Version=v1.0)
  - xamarinmac20 (Xamarin.Mac,Version=v2.0)
  - xamarintvos10 (Xamarin.TVOS,Version=v1.0)
  - xamarinwatchos10 (Xamarin.WatchOS,Version=v1.0)
One or more packages are incompatible with .NETStandard,Version=v1.3.
Package restore failed for 'ClassLibrary1'.

I created the project ClassLibrary1 as a portable class library, change the target to netstandard1.3, and cannot install any Nuget packages that show support for netstandard1.3. Same goes for netstandard1.5 and the other versions.

I just trying pulling and building the source for MailKit (a project that supports .netstandard) to verify I wasn't setting up my project wrong and am getting the same problem:

Errors in C:\Users\zone1\Repos\MailKit\MailKit\MailKit.CoreFX.xproj
    Package System.Net.NetworkInformation 4.1.0 is not compatible with netstandard1.3 (.NETStandard,Version=v1.3). Package System.Net.NetworkInformation 4.1.0 supports:
      - monoandroid10 (MonoAndroid,Version=v1.0)
      - monotouch10 (MonoTouch,Version=v1.0)
      - net45 (.NETFramework,Version=v4.5)
      - netcore50 (.NETCore,Version=v5.0)
      - netstandard1.0 (.NETStandard,Version=v1.0)
      - netstandard1.3 (.NETStandard,Version=v1.3)
      - portable-net45+win8+wp8+wpa81 (.NETPortable,Version=v0.0,Profile=Profile259)
      - win8 (Windows,Version=v8.0)
      - wp8 (WindowsPhone,Version=v8.0)
      - wpa81 (WindowsPhoneApp,Version=v8.1)
      - xamarinios10 (Xamarin.iOS,Version=v1.0)
      - xamarinmac20 (Xamarin.Mac,Version=v2.0)
      - xamarintvos10 (Xamarin.TVOS,Version=v1.0)
      - xamarinwatchos10 (Xamarin.WatchOS,Version=v1.0)
    One or more packages are incompatible with .NETStandard,Version=v1.3.

I've posted some more details here: https://github.com/NuGet/Home/issues/3433

This all worked before I reformatted with a fresh Windows installation. Am I missing something?