When I was working on a NuGet package I noticed that some DLLs (that were not supposed to be placed there) were copied into the content subdirectory of the package.
Added file 'content\lib\Microsoft.Practices.EnterpriseLibrary.Common.dll'.
And that also caused an issue:
Issue: Assembly outside lib folder.
Description: The assembly 'content\lib\Microsoft.Practices.EnterpriseLibrary.Common.dll' is not inside the 'lib' folder and hence it won't be added as reference when the package is installed into a project.
Solution: Move it into the 'lib' folder if it should be referenced.
It took me some time to figure out that NuGet copies all project items with BuildType set to Content to content directory in package. Problem was solved by changing BuildType to None.