iOS 8 doubled backup size

Right before I upgraded to iOS 8, I made sure to back up to iCloud.
The backup ended up at 4.3 GB (as always) with about 4.0 GB of that being Camera Roll.

However, after updating to iOS 8 it now shows that my next backup will be 8.1 GB, with 7.7 GB of that being Photo Library.

Why is it that the backup size doubled, and more importantly why did my photos double?
I'm not seeing anything in there that I didn't have before.

Does anyone have any idea where those ~4GB of photos came from?

 

Well, mine was unable to backup because of this – so I had to purchase the 20 GB plan.
I'll see what it says after I back it up.