When double-clicking an image file, it does not open instantly. If to double-click it the second time, it opens in two instances. This does not depend on the associated viewer (happens with both the default Windows viewer and with MS Photo Editor).
A similar, maybe related issue: when double-clickin a torrent file, the torrent downloader opens but without that file, to activate the file one has to double-click it again.
A similar, maybe related issue: when double-clickin a torrent file, the torrent downloader opens but without that file, to activate the file one has to double-click it again.