Not sure if this is a bug, but here goes.
Looking through the Glamour examples in Pharo4 I come across the Updateable Browser example.
This example has a line that, when the collection is greater than 1, shows a list tab, the title of which is List, col size printString.
This indeed comes up and shows: 'List: 2' but if you continue to add, it doesn't change. The text will change but not the title.
I came across this when I couldn't get my browser to add tabs, even though entity gets updated.
Example from Glamour below.

| browser collection|
������ collection := GLMAnnouncingCollection new.
������ collection add: 1.
������ browser := GLMTabulator new.
������ browser column: #preview.
������ browser
������ ������ act: [:b | b entity add: (b entity size + 1). b update ] ������
������ ������ icon: GLMUIThemeExtraIcons glamorousAdd
������ ������ entitled: 'Add an item in the collection'.
������ browser
������ ������ act: [:b | b entity removeLast. b update ]
������ ������ icon: GLMUIThemeExtraIcons glamorousRemove
������ ������ entitled: 'Remove last item from the collection'.
������ browser
������ ������ updateOn: GLMItemAdded from: #yourself;
������ ������ updateOn: GLMItemRemoved from: #yourself.
������ browser transmit to: #preview; andShow: [ :a |
������ ������ a list
������ ������ ������ title: [:col | 'List: ', col size printString ]; "This isn't updating"
������ ������ ������ when: [:col | col size > 1 ].
������ ������ a text title: 'Text';
������ ������ ������ format: [:col | 'Current collection: ', col printString, '. Add more items to show the list'] ].
������ browser openOn: collection

KR