Is it a bug ? :

1. Create a new micrauthesauus
2. Create a term called 'a'
3. Create a child of 'a' called 'b'
4. Modify 'a'
5. In associated terms fields, add 'b' with the combobox
6. Click on the widget for associated terms in order to open the thesaurus assistant
7. Notice that 'b' is checked
8. Select 'a' nodes, and then click on refresh
9. 'b' is now unchecked