qt 5/6 on xfce DE: hint window added to window-list every 2nd popup

• Lazarus/FPC Version: <4.0RC2 (rev lazarus_4_0RC2-59-gcf846546d8) FPC 3.2.2 x86_64-linux-qt6>
• Operating System: < Linux >
• CPU / Bitness: <x86_64>

What happens

when a hint-window popup, it added to window-list of taskbar at almost every 2nd time. found in xfce 4.16, 4.18, 4.20 desktop envs.

What did you expect

it's should not be there

Steps to reproduce

just popup a hint window, in IDE or simplest GUI app