[Pharo-project] is this correct ?

Hi! Look this peace of code: | instance | instance := TestCase new. Transcript show: TestCase allInstances size; cr. instance become: 'aString'. Transcript show: TestCase allInstances size; cr. The size of TestCase instances is always the same. Although I used become: (and changed to an instance of another class) to one of its instances. So, my main question is, is this correct ? Or the message allInstances to TestCase should not take into account the instance I sent the message become: ? Thanks in advance. Mariano