First, I'm not running Yosemite on any Macs. I only have iCloud Drive enabled on my iPhone 5 running iOS 8.1 beta 2 and my mini running 8.0.2.
I was looking in my iCloud Drive documents with an app's iCloud picker and I came across this: notice there's a folder for a "preview" app
I was looking in my iCloud Drive documents with an app's iCloud picker and I came across this: notice there's a folder for a "preview" app