Tree fails to find #term_to_expand when #parent is set

The algorithm in _taxonomy_manager_tree_get_first_path fails to find the specified #term_to_expand when the very top of the tree isn't in $tree. This occurs whenever #parent is set to something other than the top of the tree.

I spent half a day working out where the problem was, and I have spent several hours trying to debug the specific algorithm, but the lack of comments makes it pretty impossible.

Thanks,
Aidan