If you have multiple panels sharing the same area in a JFrame then you should be using a [url http://java.sun.com/docs/books/tutorial/uiswing/layout/visual.html]Card Layout[/url].
Or you need to remove the old panel before adding the new panel.
If you need further help then you need to create a [url http://homepage1.nifty.com/algafield/sscce.html]Short, Self Contained, Compilable and Executable, Example Program[/url] (SSCCE) that demonstrates the incorrect behaviour, because I can't guess exactly what you are doing based on the information provided.
Don't forget to use the [url http://forum.java.sun.com/help.jspa?sec=formatting]Code Formatting Tags[/url] so the posted code retains its original formatting.