Backspace error with line edit for Japanese

QLineEdit is not behaving correctly for Japanese input with Hiragana input mode. There is an assert failure with QString.

Steps to reproduce the issue:

• In the ‘Region and Language’ select ‘Change keyboards…’. Add Japanese Microsoft IME Keyboard.
• Launch Line Edits Example (%QTDIR%\examples\widgets\lineedits) in debug mode and set focus to the Echo line edit.
• From the Language Bar change the input language to Japanese. Also change the Input mode to Hiragana (it has the pre-edit state). Now the taskbar should have the icons shown in the taskbar.png
• Press ‘a’ key four times
• Then press space twice (the line edit will have the pre-edit string)
• Press backspace once
  -> all the characters remain in line edit, nothing is deleted. There is no event delivered to QLineEdit::keyPressEvent.

If you now continue with the following steps, you will get an assert failure:

• Press backspace four times
• Press right arrow tree times (cursor moves to right)
• Press backspace once again
  -> The application will output a debug error referring to the “Q_ASSERT(uint < uint(size()));” in qstring.h (line 679)

Attached the callstack.

If the application is run in release mode and the above steps are executed then it’s not possible to clear the last character from the line edit with backspace. See the release.png.