The cursorRectangle property for QInputMethod is not updated properly when the focus is on an input field that's at the beginning of the line.
If you try to input some characters in the "not-working" input field, the reported cursorRectangle is always (0, 0, 0, 0). I've noticed it happens when the input field is rendered as the first item on the line; for example, any input in "working-input" or "working-password" will correctly update the cursorRectangle property.
Also, notice that if you select any text in the "not-working" input field, the reported cursorRectangle is valid.
See attached example project.