I've been able to avoid this problem by replacing the start menu with Classic Start Menu, but that comes with its own set of issues (lag, funky focus interactions, and inability to launch some metro apps). So far, this is the only issue that has me thinking about downgrading.
- Start menu keyboard acceleration is poor. I used to be able to hit the Windows key and then just hit ENTER to run the first app on the Start screen. Now, you have to hit tab or use an arrow key before you can do anything.
- The Start screen/menu/whatever doesn't let you operate in bulk anymore. WTF? Now I have to click three times as much to disable live tiles for a bunch of apps.
- Why can I not middle-click task-bar items to close the app yet? This seems like an obvious feature since that's how you close tabs on a tabbed window. 7+ Taskbar Tweaker fixed this glaring omission in Windows 8, but it's not on 10 yet. (I don't combine taskbar items. I know you can click the preview window after waiting a second for it to show up, but that's too slow.)
- They removed titlebar colors from all Windows so now you can't even tell which window is active or where the titlebar can be dragged. (This is an anti-pattern obviously copied from OS X, but the reason that I don't use OS X is because I don't like most of Apple's design decisions either.)
- I can't stand all of the thick borders and focus lines in the Metro/UWP style apps. At least in Windows 8, I could avoid them most of the time but there are even more of these screens in Windows 10. Win32 apps are so much better looking than this.
In short, I'm uninstalling this and going back to Windows 8.1 Pro, which I actually liked because it was easy to avoid Metro.
Because middle-click on taskbar button opens new window/instance of application.
So, I think if we need a reason to change the functionality of middle-click on a taskbar-item, that's it. Every window should have a close-window function and there would be no confusion over what middle-click means.
(Then again, I guess the designer was probably trying to protect non-power users when they decided that. A close-window function is obviously a destructive act. But power-users are such a powerful group, so I think they need to cater to use a bit more by giving us the gosh-darn options that we want!)
EDIT: Also, I take it back. I'll keep it on this machine for now and see what happens...