Using Visual Studio 2017, create an empty VSIX project using File / New / Project / Templates / Visual C# / Extensibility / VSIX Project. Hit Build. Close Visual Studio, then install the extension by double-clicking the VSIX file in the bin\Debug folder. Start Visual Studio 2017, go to Extensions and Updates, and see that the extension is installed but disabled. It should be enabled.
This is a breakage in Visual Studio 2017 - if you follow those same steps using Visual Studio 2015, the extension is correctly enabled after restarting Visual Studio 2015.
Note that in both cases the extension is being installed by the VSIX installer, not by an external installer, and in both cases, InstalledByMsi is false.
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