Code

import QtQuick 2.15
import QtQuick.Window 2.15

Window {
    width: 640
    height: 480
    visible: true
    TextInput { anchors.fill: parent; focus: true }
}

Steps to reproduce
1. Install the Korean language (no need to install the optional language features)
2. Switch to the Korean keyboard (Microsoft IME) and activate Hangul mode
3. Run the code above
4. While the TextInput has focus, activate the Microsoft emoji keyboard by pressing [Windows] + . (see https://blogs.windows.com/windowsexperience/2018/02/05/windows-10-tip-get-started-emoji-keyboard-shortcut/ )
5. Click on an emoji character
6. Close the emoji keyboard

Outcomes

• At Step #5, the selected emoji character appears in the TextInput (expected)
• At Step #6, the emoji character disappears from the TextInput (unexpected)

Notes

• Widgets (e.g. QLineEdit) are affected too
• This does not affect the US English keyboard or the Simplified Chinese keyboard (Microsoft Pinyin, Chinese mode)