Users assigned to a team prior to staging a site are not added to a team on the staging site when a team is enabled.
STEPS TO REPRODUCE
1. Add a new site role
2. Add the following permissions to that site role:
Settings > Site: View Site Administration Menu
Settings > Site: View Staging
Web Content: Access in Site Administration
Web Content > Web Content: View
3. Add a new user and make him a member of the default site and give him the site role in step 1
4. Add a new team to default site and add the new user to the team
5. Add a new web content folder
6. Edit the permissions on the folder by only giving owner permissions and "add web content" permission for the team
7. Activate local staging on the site
8. Go to the staging site and look at People > Teams > Team created in step 2
The new user is added to the team on the staging site when staging is activated
The new user is not added to the team on the staging site when staging is activated.