Missing transitive Dependencies for specific nupkg

Description

When adding the Dropbox API as package (http://www.nuget.org/packages/Dropbox.Api/) in a C# .Net 4 Client Profile project, the transitive dependencies are missing.

Repro steps

1. Create a C# project with .Net 4.0 Client profile
2. Init Paket
3. Add Dropbox.Api to dependencies and refences files
4. The application won't compile as the dependencies are not resolved.

This is the sample project for that:
https://github.com/pdfforge/paket-bugreport

Expected behavior

The project should compile ;-)

Actual behavior

The dependencies are not recognized, most likely due to the dependency group definition:

  <group targetFramework=".NETPortable0.0-net40+sl5+wp80+win8+wpa81">
    <dependency id="Newtonsoft.Json" version="7.0.1" />
    <dependency id="Microsoft.Bcl.Async" version="1.0.168" />
    <dependency id="Microsoft.Net.Http" version="2.2.29" />
  </group>

When using the nuget manager from Visual Studio, the dependencies are added as expected.

Known workarounds

Add the transitive dependencies manually and pin them to the required version.

Start by reproducing the failure with the linked paket-bugreport sample: create the .NET 4 Client Profile project, add Dropbox.Api, and inspect the generated dependencies and references files. Compare Paket's result with Visual Studio's resolved dependencies, then verify that the project compiles without manually pinning the transitive packages.