Hi Ondo,
Please try the following.
I found this when i tried for the following issue.
First create a variable
v_max=()In Block - 2
now go to
Format filter=>
click add
select the object
click OK
now go to define
and write the following formula.
=<<v_max>
now click ok and apply.
Now we have our trick
go to the first variable
make it as the following
v_max=[b]max/bIn Block - 2.
(if we do this early BO will show error
Cannot use aggregates in complex filters).
Please let us know if this is working.
DoSTh 
(BOB member since 2007-05-31)