update-notifier pops up a notice despite an ongoing upgrade

When I invoke "sudo apt-get update; sudo apt-get dist-upgrade" on the terminal, after "apt-get update" has finished and "apt-get dist-upgrade" is about halfway done, the update notifier decides to pop up the "New updates available" notice (see function show_notification()). This is annoying and not useful because I'm doing the upgrade already. The update icon in the tray is grey, not red, so the working state of apt seems to be determined correctly, it's just not taken into account when deciding to show the notice.