Double Click on .unitypackage opens the projects window

Hello,

I literally have exactly what described here:
https://forum.unity.com/threads/win...ension-should-be-handled-by-which-exe.290911/

And to summarize:
=======================================
DEFAULT & DESIRED BEHAVIOR:
Upon double-clicking a *.unitypackage in Windows Explorer:

If either installation of Unity is already active in the Task Manager:
The active installation will handle it and proceed to prompt the "add assets to project" window for the currently active project.
Otherwise, if an installation of Unity is not active in the Task Manager:
The most recently installed version of Unity will be launched and prompt the "New Project" window[**].

BROKEN BEHAVIOR:
Upon double-clicking a UNITYPACKAGE in Windows Explorer:

If either installation of Unity is already active in the Task Manager:
A new instance of the most recently installed version of Unity will be launched and prompt the "New Project" window, disregarding entirely the presence of the currently active installation of Unity.

Otherwise, if an installation of Unity is not active in the Task Manager:
The most recently installed version of Unity will be launched and prompt the "New Project" window.
===========================================================

I've tried the solutions in that thread but it didn't help. I've tried a similar solution as described here:

The first time I've tried to fix (with the YouTube video) it was successful... but then I got a different error that the packages cannot be decompressed. So I've uninstalled unity (2017.1.03f) with Revo Uninstaller to remove any traces in the registry to have a really fresh install. Now neither of the fixes do any change and I can only import manually via the menus.

I think it happened because I also had Unity 5.6 installed and I've uninstalled but it didn't happen right away. Also the editor has no problems whatsoever to export packages.

So how can this be fixed or how do I find any traces of Unity in the registry to purge, because believe me uninstalling with Revo and re-installing Unity like 3 or 4 times didn't do the trick at all.


Unity ver: 2017.1.03f (had 5.6 installed concurrently until uninstalled on a different hard drive)
Windows ver: 10 64-bit.

EDIT: Also just noticed that after installation I got a new "Standard Asset Demo" project and it's 5.6 version even though the installer was of 2017.1. How do I get rid of the 5.6 traces? Please help.