yield return WWW stops Coroutine?

Update:

I tried replicating the scenario by writing this code and got the same results.
thisWillCheck will never be false, if internet connection is retrieved halfway.

 IEnumerator FindWWW()
     {
         while(thisWillCheck)
         { 
             print ("Still checking");
             yield return null;
         } 
     }
 
     bool thisWillCheck;
 
     IEnumerator JustTesting()
     {
         WWW www = new WWW("http://google.com");
 
         yield return www;
 
         Debug.Log("CheckingInternet now");
 
         thisWillCheck = true;
 
         StartCoroutine(FindWWW());
  
         while(www.error != null)
         { 
             www = new WWW("http://google.com");
 
             yield return www;
             Debug.Log(www);
             yield return null;
         }
 
         thisWillCheck = false;
     }

Original post:
I recently tried using "yield return www;" in my coroutine and got something unexpected.

This is my code:

 while(!checkForObject)
         { 
             //Player cancels halfway during check
             if(cancel)
             {
                 print ("stopped");
                 cancel = false;
                 yield break;
             }
             
             yield return new WaitForSeconds(0.5f);
             
             www = new WWW("http://website.com"); 
 
             yield return www;
 
             print ("Checking objects");
             
             if(www.error != null)
             {
                 print ("No connection");
             }
         }

If www is returned null at first (Internet connection lost), and suddenly returned with a value (reconnected), my coroutine will end abruptly, it is not caused by player input. It was as if it did "yield break". I tried removing "yield return www" and all things went well.

Please correct me if I'm wrong, initially I thought "yield return www" is similar to "yield return null" when www is not returning a value. But since this is happening, I doubt so.

Can anyone explain what does it actually do? Thanks in advance! :)