on iOS: when the keyboard is activated by a TextBox, it can't be activated a second time by tapping on the TextBox.

on Android the keyboard can be repeatedly activated, but because of the other (in this forum) reported TextBox bug on Android it is unclear whether it would work correctly, if the other bug didn't exist.

also, more a cosmetic issue... on iOS, the buttons on the inputbox attached to the keyboard ("Done", "Cancel") are not localized. they display in english regardless of the system language.

I guess it could be a problem with focus...

Could you make a test?
Instead of having a single TextBox in your interface, add a Button so you can change the focus between both controls (by clicking one or another).
Let me know if this way, when focus come back to the TextBox, the virtual keyboard shows up again.

i will try this on monday and let you know.