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

Inizia con la MaterialDesignXaml Demo App e riproduci il problema digitando caratteri a larghezza intera in un TextBox all'interno di un DialogHost. Analizza il comportamento del posizionamento della finestra dei candidati IME associato al DialogHost Popup. Il lavoro è completato quando la finestra dei candidati appare vicino al TextBox attivo invece che nell'angolo superiore sinistro dello schermo.