A slave vocabulary is preset from a previous request.

[sgeulette]

If you add a content type containing a master field (action vocabulary) and change the value of the master field, the slave field vocabulary is updated. Right.
Then if you save or cancel the form and call again the same add form, the loaded slave vocabulary field is the previous "calculated" one and not the "original" field vocabulary.
You can test this with collective.task product or with the masterField4 of demo.py in PR #9.