label for parent directory is not resolved in Terms aggregate

1. create a schema with a multivalued String named myMultiStr
2. create a vocabulary
3. create a simple vocabulary aVoc
4. create a schild vocabulary named bVoc referencing aVoc as a parent
5. create a custom document using a Multiple Chained Vocabulary widget
6. reference the bVoc vocabulary
7. customize the Search form and drop a Terms aggregate
8. select Directory Select type
9. select bVoc as vocabulary
10. synchronize the project with the server
11. create several docs with several values for the attribute
12. go to the Search tab
13. select a value for the field
14. observer the parent label is not resolved and only the child is

Notes:

1. doing the same with a single hierarchical vocabulary instead of 2 parent/child vocabularies works fine.
2. please see vocabAggregates.png for comparison
3. please find ffischer-710-NXP-21929.zip for fast reproduction