[Windows] Selection box in Korean input method doesn't pop up when editing existing text

When you input in Korean Han method the selection box is triggered with [Right Ctrl] key. This works when you input new text, but if you want to modify existing text by selecting a character and pressing [Right Ctrl] the selection box doesn't pop up.

This can be tested with any text edit in Qt. Add Korean Input language and choose Han input method. Then input several 'g' letters. If you now press [Right Ctrl], you can see the selection box (as you should). But if you choose one of the input characters and press [Right Ctrl], the selection box doesn't pop up.

For reference, this works e.g. in MS Word, Notepad and Skype for Business, and therefore it is requested for Qt on Windows platform.