I start a blank VS 2015 project from scratch; for this test I chose new console app. The new project is targeting framework 4.5.1. I manage Nuget packages for the solution. I look for a Nuget package recently upgraded to 4.6.1. I cannot see it as expected since my project cannot use it.
Prior to upgrading that package, many previous versions were listed as available. After the upgrade, none are available, even those targeting previous framework versions. Upgrading my test project to 4.6.1 makes the latest version and all previous versions available. This is happening with multiple packages, and the packages themselves have no package dependencies.
I am using VS 2015, Nuget Package Manager for VS 3.4.4.1321, and accessing the packages via ProGet.
Is this a known issue? Is this the way it should work? Seems like a bug somewhere to me.
For others, the resolution in our case was an upgrade of ProGet. This cleared up the original issue, but be aware that VS Package Manager will allow you to add a package targeting an unusable framework, but will not actually add an assembly reference. It just modifies packages.config.