Tutorial problem with cache

Hi I was having a look at the last exercices of the tutorial and I'm having a problem with the last exercice with custom descriptions. the custom description are doubled each time I access to them in the container... decription is overriden in MAPersonModel MAPersonModel>>description ^super description copy; addAll: self class customDescription; yourself. copy sould prevent to change the description stored in the cache. Is it correct ? This makes me ask you another question. When a description (class side) is changed, how the cache of the builder is refreshed ? I have no idea Thank you Cédrick