Its a new windows 10 problem, that I think might have popped up in a recent update. It will be fixed in the next release of OctoPrint, but for now you will have to use the command shown in the plugin repository to install plugins.
Yes - I had this problem, reported it and it was fixed a couple of months ago, however we have not had a new release of Octoprint since August and until we get one we won't get the benefit of this fix.
And of course, the whole point of Octoprint is to provide remote access, and when you have to be at the physical Octoprint server to install updates or plugins using native PIP commands, it is very annoying.
So the sooner we get a new release of Octoprint, the better.
It would be nice to get 1.5.0 out before the end of the year, but not sure where that stands at the moment.
I'm running maintenance branch for development, and it seems pretty stable to me. You could try that so that you have this fix in place.
If it doesn't happen soon, it will be in the new year, but that's not up to me.
One thing I do know is releasing too close to the holiday season can be occasionally risky, just in case there are issues - people like to spend a lot of time printing, or buying new printers/Raspberry Pis etc...
I know it is asking a lot, but getting a minor Windows only version out just with this fix would be VERY helpful as this problem really is fundamental and more than just a minor annoyance. (It could even be an unofficial build.)