Calc field in ListField property of TDBLookUpComboBox

I use a TDBLookUpComboBox with Delphi 7 and Interbase 6.1.
Can you explain this strange behaviour.
This is my sql =ABselect name||', '||surname longname, address from
table1 order by 1=BB. If I use =ABlongname=BB in the ListField  it works
fine but with =ABlongname;address=BB it does not work.  Do you know a way
to bypass this behaviour.

Thanks