Let alone that the app is abysmally slow on an iPhone 5s. Even if your inbox (not "done" emails) features 7 emails and 3 new emails come in, the app doesn't even fetch them fully and loads them one-at-a-time upon opening.
And the inbox.google.com web interface does the exact same thing! It also gets stuck for several seconds when pressing "done" on a lone email in a group, showing an empty group for a while until it realizes "oh, there are no emails in this group" and finally disappears.
The app should be SIMPLE and FAST and it is currently neither. I am really thinking about returning to Gmail fully and using some other client for iOS.