In case this is useful, Some experimenting I've done:
- Turning live tile off and on does not clear the old update.
- Closing the app and cycling the live tile does not clear the update.
- Hard closing (right click the sidebar item and "close") and cycling live tile does not clear the update.
- Unpinning app and repinning and then cycling live tile does not clear the update.
To try next:
- Put computer into sleep mode.
- Reboot.