Not being catty, but that's a workaround (which is appreciated) but apple needs to fix this.
I'm having the same issue on my 6+ 64gb.
I've noticed it often happens when the phone was locked but here's the weird thing. The phone isn't just stuck in the current screen orientation, it seems only the home screen is. If the home screen is stuck in upside down portrait (probably from being upside down in my pocket) but I launch an app, holding the phone right side up, the app opens right side up, but if I hit the home button, the home screen is still stuck upside down.
As others have pointed out, if I leave the phone alone and don't do anything, it eventually fixes itself.
There seem to be a lot of bugs like this in iOS8... Does not feel polished at all. That's a shame.