[SalesForce] Cases related list on Opportunity for person account shows the same cases

I wanted to have an ability to associate an case with an opportunity. So i created a lookup field on cases to opportunity and added the cases related list in opportunity page layout.

The issue i am facing is that when i add a new case for a opportunity lets call it OppA. I can see that case reflected on the cases related list of OppA. If there is another opportunity(OppB) using the same account, this case is visible on that opportunity as well.
Is this a standard behavior? Should i need to write a custom code to get only cases related to a particular opportunity?

Account used is a Person account( Not sure if that makes a difference)

Best Answer

There is a standard Cases related list available for Opportunities that shows all Cases for the Opportunity's Account (http://help.salesforce.com/apex/HTViewSolution?id=000004153&language=en_US). You probably added that related list to the Opportunity layout instead of your custom one. Edit the layout and see if there isn't another Cases related list there that you can add - that'll be your custom one. You might want to edit your custom lookup field and change the name of the Related List Label to differentiate it from the standard one.