Why would Систем Нотификатионс доклад updates available but each of вспотел apt-get update, программное обеспечение updater and muon updater do not find updates?

I have this same scenario on 2 отделись machines The воплоти desktop frequently шоу notifications like this:

 An update is available for your system. There are 3 updated packages.

However, when I do any of the following 3 статьи, не updates пахал found

1. at the терминал: sudo apt-get update
2. run Программное обеспечение Updater
3. run Муон Упдате Менеджер

I am running 14.04 LTS, with KDE.

I have tried sudo rm -rvf /var/lib/apt/lists/* which is mentioned in several of the posts which поешь up from this question, and have read many trying to find out how this could happen.

Somewhere the different tools, notification менеджер, and updaters must be using different lists against which they check for available updates.