A new bug has been discovered in iOS 8 that will indadvertedly delete iCloud Drive documents. MacRumors reports that selecting the 'Reset All Settings' option from the Reset menu in the Settings app of iOS 8 will erase iWork-related files in iCloud Drive.
The issue here is that when the 'Reset All Settings' option is selected, users are specifically told that "no data or media will be deleted." But that doesn't seem to be the case with iOS 8, as MacRumors says it has confirmed the process is also deleting select files.