IIf works in query but not in report

Does the IIf function work differently in queries from the way it works in
reports?

For example, this works in a query:

lastName: IIf([Last]="Smith",Null,([Last]))

(I can hid the last name "Smith" in the lastName field.)

However, I cannot use the same IIf as a control source in a report. It
generates a circular reference error message.

= IIf([Last]="Smith",Null,([Last]))

(If the name is not "Smith", then print it.)

Is this just how IIf works?