IME input deletes characters to the right of the cursor when typing Japanese full-width text

[jagio0129]

When typing Japanese full-width characters using an IME,
characters to the right of the cursor are unexpectedly deleted.

This happens even when typing on the official demo page:
https://react-email-editor-demo.netlify.app/

It looks like characters are being removed as if the editor is in overwrite mode,
but overwrite is not enabled.

1. D&D Heading.
2. Move the cursor into the middle of the text(between "a" and "d").
3. Start typing Japanese full-width characters using an IME.
   • erase "d"

Expected Behavior

New Japanese text should be inserted at the cursor position.
Existing characters to the right of the cursor should remain intact.