To reproduce:
- run the attached application on Windows 11
- change the input language to Japanese/Hiragana (あ shows up in addition to JP in the windows toolbar)
- type in 'a'

Upon first launch , the IME window appears in the bottom right corner instead of near the text field. Dismiss, type - the windows appears where it's supposed to be.

See also
https://github.com/openjdk/jfx/pull/1337#issuecomment-1901265779

Contrary to this comment
https://github.com/openjdk/jfx/pull/1337#issuecomment-1901527510
the issue cannot be reproduce with JTextField in a regular JFrame, so it must be related to JFXPanel.