Taxonomy parents need to be saved before term hooks are called

Hi, I'm a beginner. I've just installed Drupal 7 with XAMPP on Windows XP. I've created a vocabulary (myvocabulary) with many nested terms. With Pathauto I would like to create urls such as www.example.com/parent_term/child_term.

In "Configuration » Search and metadata » URL aliases" I've set "Pattern for all myvocabulary paths" to [term:parent]/[term:name].

I've enabled also "Bulk generate aliases for terms that are not aliased".

Here is what happen when I hit the button "Save configuration":

1. All existing terms which do not already have aliases get a new correct url www.example.com/parent_term/child_term

2. When I create a new child term in the vocabulary, it get the wrong url www.example.com/child_term (In other words Drupal can't fetch the parent term for new child terms)

Is it a bug?

Note: sometimes when I apply a new URL Pattern in "Configuration » Search and metadata » URL aliases" with the option "Bulk generate aliases for terms that are not aliased" active, I get the following message:

The configuration options have been saved.
Bulk generation of terms completed, 23 aliases generated

Notice: Trying to get property of non-object in taxonomy_tokens() (line 141 of C:\xampp\htdocs\example\modules\taxonomy\taxonomy.tokens.inc).

(This last error message is repeated many times)