Is the second case handled by the "frontend"? Shouldn't be handled by the backend and then return an error state/message?
It's not as simple as cases where both data and logic are local to the gui.
In this identified case, the gui has to react/behave correctly according to the results/errors of asynchronous remote logic over a spotty network.
For example:
You're loading or submitting content asnychronously and must handle different loading states in order to give the user feedback. If an action fails due to spotty internet you must also include a retry or refresh button.
You load a model form to modify some data, and when you submit your changes someone else has already made modifications to the model.