This was one of the OOPSLA / Camp Smalltalk 3 fixes.

>From the preamble:

Change Set:		CS3-ScrollBarPositionFix
Date:			5 November 2000
Author:			Doug Way, Camp Smalltalk 3 @ OOPSLA

Fixes a longtime problem with updating the position of the scrollbar
when the contents of a scroll pane increases or decreases significantly
in length.  Basically, the scrollbar position was not being updated
before, and now it is.  Also refactors things so that
SimpleHierarchicalListMorph>>setScrollDeltas is removed.

(The bug is easiest to reproduce in an object explorer, if you expand
things and scroll down so that the scrollbar thumb is in the middle of
its range, and then expand an item in the explorer which has a lot of
children.  Then if you click on the up arrow in the scrollbar, the pane
will skip to the wrong place because the scrollbar position hadn't been updated.)
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