Turn "max amount" in the amount selection into an option instead of copying the amount

[janklosowski]

1. I want to send all my coins so I press "Max" while typing the amount.
2. The fee seems to be high so I manually pick a lower one.
3. I press "Send".
4. Unfortunately, my wallet is not empty: the amount I supposed to save is still there because I forgot to press "Max" again to update it.

This is a very confusing UX. I'm sure many people do this mistake using custom fees and it cost them extra money or even makes the remaining amount unspendable in many cases.

Proposed solutions:

1. In my mind, when you press "Max", it's rather obvious that you're not interested in sending an exact amount since you cannot know it before including fees. So, I would rather adjust the amount to the new maximum. It could be even clearer with the "Max" button working as an ON/OFF switch that stays highlighted until you manually change the amount.
2. The other option is to clear the amount after changing the fee, so the user is forced to enter it again. A bit less smooth experience but also addressing the case. Some short message why it is necessary would be a good idea.

[Giszmo]

It actually is an issue in both directions. If you want to empty an account and change the fee after picking the amount, you either leave dust behind or you are blocked from increasing the fee without another round-trip to the amount screen.

As you said, picking "Max" should be opting for "send all", disabling the amount entry. Checkbox style.