The same thing happens w/ the FB webapp, so my comment is in this context. After the OA login prompt is gone, I am not able to have the OSK popup again...
BUT
... it does work as expected when I right edge slide the app a bit to make the "switcher" appear and release the touch so that the app goes back into focus. After that touching a text field makes the OSK appear again.
This trick works very reliably and seems to point at a window/app focus issue after a trusted session ended.
The same thing happens w/ the FB webapp, so my comment is in this context. After the OA login prompt is gone, I am not able to have the OSK popup again...
BUT
... it does work as expected when I right edge slide the app a bit to make the "switcher" appear and release the touch so that the app goes back into focus. After that touching a text field makes the OSK appear again.
This trick works very reliably and seems to point at a window/app focus issue after a trusted session ended.