Why can't you just detect that it was already signed with a valid signature, especially if you have the user's public key?
PS: the lack of threading support in your mobile apps is embarrassing, it's been like this for years. No I will never use your web client. Stop trying.
Correct. You lose customers on purpose when you don't have basic features that the competition has had for years, and when, after years of delays, you release a new version of your app that still doesn't have this feature.
I don't know why you think this is some sort of gotcha. Other than you think having standards is too entitled.
PS: the lack of threading support in your mobile apps is embarrassing, it's been like this for years. No I will never use your web client. Stop trying.