Tested on Nexus 7 running Android 4.4 using QuickOffice 6.2.5.310b.
I've written a DocumentsProvider and testing integration with QuickOffice. In QuickOffice, I click Open, choose my provider, and select a file. I edit the file and click Save. If an error occurs uploading the file to my cloud server, QuickOffice displays a toast that the file was saved successfully and doesn't display the error. I'm using ParcelFileDescriptor.closeWithError().
It's a known issue with QuickOffice:
https://code.google.com/p/android/issues/detail?id=65642