i accidentally catched this, at first i thought of file corruption
Color management is OFF (turning it on does not help). Files does not have alpha channel or transparency.
Old version of XnView (with the same config) does not show this behavior.
OS: Windows 11 25H2 HiDpi mode ON
how to reproduce: just run XnView and go to folder with such files.
I attached some screeenshots to clarify.
I also attached the files causing bug. (ned.jpg and RosenKatze.gif)