The user-expected behavior on a touchscreen-equipped device (especially, but not exclusively, "convertible" tablet/laptops with keyboard docks) is for a virtual keyboard to pop up on the screen when text input is in focus and a hardware keyboard is unavailable.

Instead, current and past versions of GNOME appear to make Caribou pop up whenever text input is in focus and the last pointing device to be used was the touchscreen. The virtual keyboard disappears only if a different pointing device (e.g. a mouse or touchpad) is used or text focus is lost; it does not even disappear when a physical key on a physically connected hardware keyboard is pressed.

I presume the current behavior originated in the assumption that when a touchscreen is in use, a device is likely in a "tablet"-style mode; however, that is only an indirect inference, while a much more direct test would be to check for presence of a physically connected keyboard, or at the very least (in case glitches in keyboard detection make such a test unreliable) to check for hardware keypresses actually taking place on such a keyboard.


In conclusion and to simplify: currently, Caribou is brought up when the screen is touched, and hidden when a non-touchscreen pointing device is used, irrespective of hardware keyboard presence or state; however, with the exception of accessibility modes, users would not normally want or need a virtual keyboard unless a connected and functioning hardware keyboard were unavailable, irrespective of touchscreen presence or state.