framework: auto-detect problem

[marcinbudny]

When using framework: auto-detect in paket.dependencies in a C# solution, when conditions specified below are met, following error message appears:

Paket failed with:
        Package Autofac  - framework: net452 was referenced, but it was not found in the paket.lock file in group Main.

The conditions:

• Solution depends on the Autofac package (probably this happens with other similar packages as well)
• Solution also depends on another package X. Package X depends on Autofac. Package X is in a custom feed (not the official nuget feed)
• Solution has more than one project. Projects target .NET 4.5.2

Problem does not occur on the initial paket install run (when no lock file is yet present). However it occurs on any subsequent paket install run.

If I use framework: <= net452 instead of framework: auto-detect, all works well.

I created a repro for this problem here: https://github.com/marcinbudny/PaketFrameworksProblemRepro

I'm using Paket version 2.51.7.0