I have posted an item on Qt forum. Here is a summerise:
1. Enable virtual keyboard for the project in main.cpp;
2. Create a QLineEdit on a popup dialog;
3. Set a validator for the QLineEdit, for example, a QIntValidator;
4. Let the QLineEdit got focus, enter out of range characters, such as ‘a', 'b', 'c' from the physical keyboard.
The program will crash when doing step 4 on Windows 10. But the same program works well on Ubuntu 18.04.