Having the Browser open and viewing a photo in the 'preview' pane, and I restore the modified file from a backup, xnview does not update the image in the 'preview' or the 'exif' data or anything else until I click on a different file and then click back to the file in question. I think it should be updated when press the F5 key.
Also, sometimes the thumbnail does not update either, and requires view->rebuild thumbnails option, but sometimes it does update without that.