As discovered by MacRumors and also mention by Appadvice (from where I got the information) users that have used the "Reset All Settings" option that it is found on (Settings > General > Reset) in your iOS device may erase all their all their iWork Documents in their iCloud Drive. Obviously this seems like a bug, and Apple may fix it in the next iOS 8 release.
As also mention by Appadvice:
This is particularly worrisome for users of iOS 8 and OS X Yosemite. If you use both and this happens, your data will get erased, then sync across devices, and erase from them as well.
Make sure if you are using iCloud, iOS 8 and OS X Yosemite to have your files backup, do not trust iCloud since as far as my knowledge goes, there is no backup function for the documents you have there, so be careful.
Posted on Tuesday, September 30, 2014