A correct observation but anyone for whom this matters understands (or 
will learn very quickly) that #allInstances is a utility method that 
cannot possibly give the correct answer in all situations. You have 
found one, but there are others (hint: think about method activation).

The only true way to find all instances of some class is to do it 
yourself at the place where you need it, like here:

obj := aClass someInstance. 
[obj == nil]
 	whileFalse:[ obj := obj nextObject].