Selected option doesn't show properly in editing node page

I have this taxonomy hierarchy for instance:

Product A
- Brand A
-- Model A
-- Model B
- Brand B
-- Series A
-- Series B

I created a new node and chose "Model B", the module works well when first creating the node, one display after another. However, later when editing the node again, I realised it only show:

Product A > Brand A

Which the last Model B was not in the select hierarchy. Of course I know what I chose, but if the next webmaster login to edit, he won't know which Brand I have chosen. Any insight?