Fwd: do:displayingProgress: Question/Problem

Hi all I detected a behavior and Im not sure how to classify it (most sure is ignorance :P). Maybe some one can explain me.

Given the code:
Smalltalk allClasses
            do:[:aClass| (Delay forMilliseconds: 1) wait]
            displayingProgress:[:aClass| 'Processing ', aClass name].

(Which is the example on the Collection class)