Thank you for your feedback.
1) This is correct. Internally, when a TabItem is removed, we do not set its content explicitly to null. This scenario should be handled internally by the ItemsControl, the TabControl should generally modify the Content of its items. If the content is long-lived the TabItem should still be garbage collected if there are no other items.
2) TabControl has a new property called PropagateItemDataContextToContent that indicates whether the data context of the TabItem should be assigned as DataContext of the content area when the selection changes. The default value of the property is true. Try setting it to false and let us know if you are still experiencing issues.
3) You are correct that TabWrapPanel holds a list of the TabItems, but this list gets cleared on each measure / arrange. The measure / arrange pass after the items have been cleared should release them from the panel as well.
There is a memory leak with the templates in SL4, I am not sure if this applied in your case but it may be good to know:
We well be happy to investigate the memory leak in your particular case if you can send us a project that reproduces the problem.
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