I found a problem with profile2. This is what I do:
1. I created a field on admin/config/people/accounts/fields
2. I created another field on admin/structure/profiles/manage/main/fields (profile2)
3. On admin/config/services/mailchimp/lists/1/edit I assigned both fields to merge tags from my mailchimp list.
4. I created an user and only the first field was added on mailchimp.
5. I go to the new user edit page and click on the save button without changes, and this time the data from the second field appeared on mailchimp.
There is something I'm doing wrong or this is a bug?