What is the proper way of retrieving and handling sessions when making multiple calls to the API? I can't log in consistently via Services 3 in Drupal 7.  

POST http://&lt;mydrupaldomain&gt;/services/user/login.json
{
"username":"admin",
"password":"password"
}



The first time I make this request I get a session name and id back.
Which is what I want. I use the session information to make
successive calls such as update user. 
The second time I make this
request the response comes back as HTML for the login screen.  
The third time I get



  401 Unauthorized: Access denied for user anonymous



And at the forth time I get am able to login again with a NEW session name and id. 


I make these requests within seconds of each other. I will have an application which will be making multiple API calls to Drupal per second.  This includes creating a user and updating a user both of which requires that I get a user session id in order for the request to be served by the API. 

Questions:  Why the inconsistent behavior? On each login attempt I expected to get either a new session info back or, if the user is already logged in, the current session.  

What is the proper way of retrieving and handling sessions when making multiple calls to the Services API?
Apparently the Services module submits a form in order to log a user in.  I expected /login to purely go through the backend.  

Having said that, I disabled a module which hooked into my login form and now I am getting the expected results.