Problem Add User to Group after to delete the user - SharePoint 2013

Hi,

I have a ETL that add users to SharePoint(2013) group.

When I add the user "A", it's works fine. When I delete the user "A" and after run again the ETL code, the user "A" isn't inserted, but no problems ocorrurs in method (webservices) AddUserToGroup.

After, when insert other user "B" it's works. So, I isert the user "A" again and it's works perfectly.

This is a SharePoint Bug? has anyone this problem?

Thanks!!

Everton

Web_Reference_Folder_Name.UserGroup usrgrpService = new Web_Reference_Folder_Name.UserGroup();
usrgrpService.Credentials= System.Net.CredentialCache.DefaultCredentials;

usrgrpService.AddUserToGroup("Group_Name","Everton Batista","TEST\everton","everton@test.com","Notes");