Cubase 4 brackets and braces

I have a problem. I have two staffs. When the top staff is polyphonic and the bottom staff is single, I can add a bracket or a brace to both of them. However, when the bottom staff is also polyphonic, the bracket or brace only appears on the top staff - even though I drag the symbol to include them both. Does this happen to anyone else? Is there a setting I am missing?