Hey,
This is a feature but it had side effect problems. For instance, in the inspector you can see twice the instance variable of that name, 1 being nil and the other one having the correct value.
Therefore in Pharo 3.0 with the new class builder / object layout this feature was removed. Now your code will raise an Error (DuplicatedSlot) and you cannot save your class any more (a popup with the error is shown). The error tells you which instance variable is duplicated so you can fix it by removing the duplicated instance variable and saving again the class.