Currently if editing a file in Drive with an external application (Libre Office, AndrOpen Office, etc) there is no way to save the file. I have to "Save As", delete the original and rename the new one. Contacted support and was given the usual "This is how it is, it may be fixed in a future version¨. I say this is a bug that should have been caught in alpha testing and frankly I'm shocked that I'm the first to mention this here.