IME input problem

When adding a comment to a source code in Japanese (IME input),
letters that are input with "Shift +" disappears as soon as Shift is released and cannot be confirmed. This makes impossible to use characters like ? or #, for example.

This problem does not exist in QtC5.0.3 or Qt6.0.1 built by Qt5.
Also this happens on Windows but not on macOS. ( Haven’t tested in Linux )

Here is how to reproduce
1. Open any source file in Edit mode in Qt Creator
2. Add "//"
3. Switch input mode to Japanese Hiragana mode

4. Type 'a', 'i', 'u' then Enter --> This will output あいう

5. Press SHIFT key and type "hello!" ( Keep the shift pressed all the time )

Expected result
Once Shift is released, you can choose hello! from the candidate list and confirm.

Actual result
Letters with Shift (i.e. "hello!") disappears.