SQL & PL/SQL

Hi all, just experimenting with the Model clause using:

Oracle Database 11g Enterprise Edition Release 11.2.0.2.0 - Production

this:

with t as (select 1 num, 1 lvl from dual)
select num, f1
  from t
MODEL
   dimension by (lvl)
   measures (num f1, num f2)
   rules iterate(3)
       (f1[any] = f1[cv()] + f2[cv()]);

works fine

this:

with t as (select 1 num, 1 lvl from dual connect by level <= 1)
select num, f1
  from t
MODEL
   dimension by (lvl)
   measures (num f1, num f2)
   rules iterate(3)
       (f1[any] = f1[cv()] + f2[cv()]);
              

results in

ORA-32614: illegal MODEL SELECT expression
32614. 00000 -  "illegal MODEL SELECT expression"
*Cause:    An expression other than MODEL aliases, constants,
           or expressions of the two is specified in the
           MODEL SELECT clause.
*Action:   Reformulate the query, perhaps nesting inside another SELECT.
Error at Line: 2 Column: 7

what's going on?