I am using Ubuntu 12.04.

Many time I have opened the Ubuntu Software Center and noticed that software long installed shows up as not installed. I have also noticed that some software to be downloaded have duplicate entries. I find this frustrating at times. Which do I download? I have used Synaptic when I had no clue. I know that it has nothing to do with updating the apt list. As I said, some of these programs have been installed for months and I get updates regularly and have manually updated the list from the terminal many times.

Can anyone explain this or put forth a solution.