[eclipse-users] something i didn't understand about labeling?

Hello, i have a strange problem in a clp program i am writing.
(As it solves a rather complex problem -steiner tree- i tried, 
successfuly, to reproduce it in a more simple kind of application before 
asking you for clarification.)
Here is the code http://avanguardie.netsons.org/prova.ecl
As you can see it should return the values of the elements (given a 
4..10 range of values) of a matrix, in which we want that the sum of the 
elements of one specified (in this case the 1^) row is the smallest 
possible, given that it can't be smaller than a precise number (in this 
case 2).
When i call the goal prova(X), the cost provided is correct (8); X, 
instead, is returned as an uninstantiated (barely arc consistent 
probably) matrix and a delayed goal is reported, exactly as if i didn't 
put in my code any labeling.

Probably it is a trivial thing that i should already know, so i thank 
you in advance for your patience, but i really can't get out of it.

-- 
M.C.