I've just tried this on Natty, selected a package, then clicked mark all upgrades, and the upgrades were selected, and the package I've selected was still selected, so the problem is not that Mark all upgrades clears the selection, but that the Reload clears the selection, just as Steven Danna commented in comment #4.
I've just tried this on Natty, selected a package, then clicked mark all upgrades, and the upgrades were selected, and the package I've selected was still selected, so the problem is not that Mark all upgrades clears the selection, but that the Reload clears the selection, just as Steven Danna commented in comment #4.