I guess you still need to do that and in worst case also some extra JavaScript stuff for value attribute change …
The JavaScript client is always the source of truth for current input values. For any given input with focus, LiveView will never overwrite the input’s current value, even if it deviates from the server’s rendered updates. This works well for updates where major side effects are not expected, such as form validation errors, or additive UX around the user’s input values as they fill out a form.
Source: https://hexdocs.pm/phoenix_live_view/form-bindings.html#javascript-client-specifics
I had the very same problem with textarea, see:
