If a component is destroyed, it and, if it is a container, all its items, are removed from Ext's component manager registry. But there are cases when components fail to be destroyed:
If two items of the same container use the same itemId, Ext does not complain, but one of them is kept even if the container is destroyed.
Components that are created manually via ComponentMgr.create() have to be destroyed manually unless they are added to the items of a container.
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