This is the fix posted by Tim Olson with the right email tag.
Seems to work with the last Squeak 3.6

-- 
Serge Stinckwich                                         -< )
Université de Caen>CNRS UMR 6072>GREYC>MAD                /~\
http://www.iutc3.unicaen.fr/serge/                       (/  |
Smalltalkers do: [:it | All with: Class, (And love: it)] _|_/
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'From Squeak3.5alpha of ''7 January 2003'' [latest update: #5168] on 23 July 2003 at 5:56:42 pm'!

!PluggableListMorph methodsFor: 'events' stamp: 'tao 7/23/2003 17:56'!
mouseLeave: event
	"The mouse has left the area of the receiver"

	super mouseLeave: event.
	self changed. "redraw to remove focus frame rectangle"
	Preferences mouseOverForKeyboardFocus ifTrue:
		[event hand releaseKeyboardFocus: self]! !