isolating TaskPanes between documents
 

I have written a custom TaskPane that is visible when a button in the Ribbon
is clicked. The functionality of the Ribbon and TaskPane work as expected.

The TaskPane contains a Label and Button. When the button is clicked the
label is updated. All works fine.

If I open two Excel documents and open the custom TaskPane in each and then
click the button on one of the Excel documents the label is updated in both
open Excel documents. The update of the label is not isolated just to the
document that caused it to be updated. This sort of makes sense because the
TaskPane is the same in both documents but I kind of thought each would be
isolated from each other.

Is there something I'm missing that would isolate the TaskPanes from each
other? Or any advice that anyone can give me on whether this is correct
behavior is greatly appreciated.

Thanks