Subject Master/Detail with readonly master

I'm using an IB_Query as master and an second IB_Query as detail.
Anything works fine. Now I'm using an IB_Grid to Display the Master an
an second to Display the Detail. The Display is correct.
But if i have more Detailrecord than grid lines an i try to scroll the
grid, i get an exception E_DatasetCannotScroll.
As I see it is because me Master is readonly. But why it is so? Is
this a bug?
An suggestions are welcome