Take a look at this package:
It shows "Windows 0.0" for the NetCore45 section.
1) Shouldn't be 0.0
2) Equating Windows with NetCore is a limiting decision and it's not accurate. Windows == WinRT. Not all Win8 libraries/packages are NetCore.
Given the amount of confusion already in the community, I'd suggest trying to be more explicit and calling it "NetCore 4.5" and leaving "Win8" references for Windows Runtime components when they're eventually supported.
Nice catch - thanks!
Status update - this appears to be an issue in VersionUtility in NuGet.Core.
Looks legit, but a client bug. Let's file it there and then close this out.
Reported in Client: http://nuget.codeplex.com/workitem/3074