Error using bind variables defined by the Define statement: "ORA-00904: Invalid Identifier" (4302884)

When the following code is executed an "ORA-00904: Invalid Identifier" is displayed:

define xdate = to_date('18-jan-2008');
select * from tablename where columnname = &&xdate;

Set Scan ON option is toggled on. Code executed successfully in 5.5.4.

WORKAROUND:
With "Set Scan ON" option turned ON, use the colon character ":" instead of the Define statement to define values of bind variables.

select * from tablename where columnname = :xdate;

STATUS:
Waiting for fix to be released in a future version of SQL Navigator for Oracle.