[Bug Bash] The package source will switch to ‘nuget.org’ automatically after installing a "PackageReference" package from a source other than ‘nuget.org’ in a non-SDK style project

[ZheeYoong1125]

NuGet Product Used

Visual Studio Package Management UI

Product Version

NuGet Client Dev\6.14.0.49

Worked before?

It is a regression since the issue reproes on D17.13\35825.156 with implicit NuGet 6.13.2.1, but doesn't repro on D16.11\35818.1 with implicit NuGet 5.11.6.4.

Impact

It bothers me. A fix would be nice

Notes:     

1. The repro rate is 100%.   

2. It doesn’t repro when installing the package with “Packages.config” format. 

3. It doesn't repro when the package is first installed using the "PackageReference" format.

4. The issue only repro when the package is first installed using the "packages.config" format and then uninstalled and reinstalled using the "PackageReference" format. 

Repro Steps & Context

1. Create a C# Console App project (.NET Framework 4.8.1).

2. Open Package Manager Settings dialog through menu Tools->NuGet Package Manager->Package Manager Settings. 

3. Click the Package Sources tab, and add a custom feed source, type in the name is “Myget” and the package source is https://www.myget.org/F/andy-nuget-project/api/v2. 

4. Check the “nuget.org” in Settings->NuGet Package Manager->Package Sources. 

5. Check the “Prompt for format selection on first package install”, select “Packages.config” in the “Default package management format” drop-down list and click OK button. 

6. Go back to PM UI -> Select the package source: “Myget” near the gear button.

7. In the “Browse” tab, select a package and click the “Install” button.  

8. After that, click the “Uninstall” button and click the “Install” button to install the package with “PackageReference” format.

9. Observe the package source dropdown box.

Expected:  

The package source should be consistent with the one when installing the package. 

Actual:  

After installing the package with “Package Reference” format, the package source will switch to different one as the record below.

Verbose Logs