Sorry I wasn't specific, the iPhone 6 plus only flips around on the standard display zoom. When on the zoomed display zoom it will not flip.
Really? Interesting, didn't know that.
I wonder if the reason I've had a lot of upside down home screens yesterday and today is related to 8.1.3. I only updated yesterday, always wait a couple of days now. I know previously my 6 Plus stubbornly refused to rotate occasionally, and I wonder if they've upped the sensitivity.
If it continues with the same frequency I'm going have to use rotation lock more, which is annoying as I often use landscape keyboard and photos.