I'm working on a solution that has multiple C# projects. One of these projects already uses a NuGet package (e.g. Newtonsoft), correctly declared as such in the packages.config file and in its csproj file.
When working on a different project inside the same solution and making reference to a class/interface that is in the aforementioned NuGet package, ReSharper accurately suggests to add it as reference.
However, when accepting this suggestion, the end result is that the reference is only added to the csproj file and not to the packages.config file. It is important to mention that I'm not using the new csproj format which has PackageReferences and collapses all NuGet data into that single file.
In this article, you can see that this was actually a problem with ReSharper some time ago and it was solved with a plugin:
However, since version 9.1 this was deprecated since it was supposedly included in the main ReSharper product:
https://github.com/JetBrains/resharper-nuget#deprecated
PD: I'm using VisualStudio 2017 and ReSharper 2017.2.2.