DialogHost: IME Candidate Window Appears at Top-Left of Screen When Typing Full-Width Characters in TextBox

Bug explanation

When typing full-width characters (e.g., Japanese) into a TextBox displayed within a DialogHost, IME candidate window appears at the top-left corner of the screen instead of near the TextBox.
This significantly degrades the user experience.

Expected Behavior
The IME candidate window should appear properly near the TextBox being used for input.

Reproduction
This issue has been confirmed to be reproducible in the MaterialDesignXaml Demo App.

Potential Cause
This issue might be related to a known WPF problem concerning IME candidate window positioning within Popup controls, as DialogHost internally uses Popup. Popup controls do not have a clear owner window like standard Windows, which could prevent the IME from determining the correct display location.

Version

5.2.1

Comienza con la MaterialDesignXaml Demo App y reproduce el problema escribiendo caracteres de ancho completo en un TextBox dentro de un DialogHost. Investiga el comportamiento del posicionamiento de la ventana de candidatos de IME asociado con el DialogHost Popup. Se considera terminado cuando la ventana de candidatos aparece cerca del TextBox activo en lugar de en la esquina superior izquierda de la pantalla.