A client reported the Who's Online was not showing active carts. I checked and confirmed. In this screen shot you can see the active cart but the icon is red for not active cart.
https://screenrec.com/share/izysTcQfMW
I searched and didn't see this mentioned in any thread or in the known bugs for 1.5.8 so not sure it's been noted before.
I checked another 1.5.8a site and see the same thing.