Virtual keyboard may not work correctly if QT_SCALE_FACTOR is set to any number other than 1.

This case can be reproduced easily by following steps:
    1. export QT_SCALE_FACTOR=2
    2. export QT_IM_MODULE=qtvirtualkeyboard
    3. Open some qt application which contains some QLineEdits or something like this,
        and click on it to let the virtual keyboard pop up.
    4. Try to click the keys on virtual keyboard, the virtual keyboard will disappear immediately
        if the position you click on is over 1/2 of your screen size.