Some time ago Memrise app changed the way it deals with the Android virtual keyboard.
Used to be
If the virtual keyboard was activated during entering the answer (i.e. the user clicked on the edit area), it would appear automatically next time in the same review session.
It can be considered as a regression by some users and can be called a bug.
The virtual keyboard is never shown automatically.
I know, people would complain in the both scenarios. In the first case, it’s annoying if the keyboard was used just for a minor fix in the answer. In the second case, it’s annoying to activate the keyboard every time if its use in intended.
You already have a button to show the keyboard if text input is requested. That button can be changed to be a toggle button. It can remember its status until unclicked.
I believe, this solution would satisfy everyone’s needs re virtual keyboard. That would especially make sense, since you prefer us to use the app, not the web site. And the absence of virtual keyboard pushes users to the web site if they want a stricter testing.