Filter showing Duplications

Hi,

I have a system set up category called Status Code, which explains the reason a lead was won, lost or still open. For some reason this field is not filtering properly and showing duplicates when i try to filter. Example below:

Even is you pick all three options of status code E.g. "Please Choose an Option...." they all have the same status of open so therefore the filter should only show this once not three times. Example below:

Is should look like this and only show the filter option once. Example below:

Can someone please tell me why this is happening and how to fix it? Or is it a bug?

Thanks, 

Margeaux.