I assign one provider for one service, but all of them become busy

I've followed your tutorial about entering and editing Appointments but found what I think is a very big problem when making a reservation from the backend (as shown in your tutorial). Steps are as follow:
Start by adding a new appointment. Then fill data and choose a provider (avoid "no specific provider" option). Save the new appointment and a succeed message is shown.
The appointment is shown as selected: client, date/time, service, provider and status are ok.
Then I check the requested service provider schedule in frontend, using [app_schedule worker="3" service="0"] shortcode and he is busy for the selected date and time. I check my other provider (who was not assigned for the service) using [app_schedule worker="2" service="0"] shortcode and he appears to be busy for the same date/time.
I assign one provider for one service, but all of them become busy.
What am I doing wrong?
Please help, there is a job I need to finish.