Problem with deleting a value from an infGraph

Hi,

I builded the ontology from the software Protégé. I developped a method with
Jena API  to delete a value inside the ontology:

public void delete(Node measurement, OWLDatatypeProperty property, String
value) {

        Node propertyNode = Node.createURI(property.getURI());
        Node valueNode = Node.createLiteral(value);

        infGraph.delete(new Triple(measurement, propertyNode , valueNode ));
    }

This method works correctly.
For example there is an instance which has a dataType property "hasValue"
and it contains the value "France":

*http://www.cmf.com/Ontology.owl#PCountryMeasurement @
http://www.cmf.com/Ontology.owl#hasValue "France"*

After executing the method above, the value is correctly deleted.

But when I launch Protégé, and I save after rewriting the same value
deleting "France" , I execute this same method but this value is still here..

Actually, when I change something in the ontology graphically with Protégé,
I can't delete it with the method above.

I printed the statement to see what is the problem and I saw this statement
after rewriting the same value graphically.

*http://www.cmf.com/Ontology.owl#PCountryMeasurement @
http://www.cmf.com/Ontology.owl#hasValue "France"^^
http://www.w3.org/2001/XMLSchema#string*
*
*
There is something added to the second statement compared to the first
statement: *^^http://www.w3.org/2001/XMLSchema#string*
*
*
Is there anyone who can help me please?

Thanks