The size of the Properties/Histogram/EXIF panel in the preview pane is not saved: if you resize it, the new size is lost upon restarting XnView. This happens at least with the fourth layout from the top (View|Layout menu), e.g. tree folder on the left, thumbnails on the top right and preview on the bottom right.
I could not reproduce this problem. The size of the preview and Properties/Histogram/EXIF pane is stored and restored properly. I've tried layout 4 (which is default).