Hierarchical terms have inaccurate node counts.

Issue Summary

My term hierarchy looks like this, and uses dynamic selects to ensure that people will select both a parent term and a child term:

* A
** A1
** A2
* B
** B1
** B2

Now I have 4 nodes tagged A and A1, 2 nodes tagged A and A2. What sitemenu should therefore display is:

* A (6)
** A1 (4)
** A2 (2)
* B
** B1
** B2

What it displays in fact is:

* A (12)
** A1 (4)
** A2 (2)
* B
** B1
** B2

I guess it inaccurately counts child terms twice.