Can Unity WWW http requests scape from the capturing by tools like httpscoop or Charles?

I do several WWW http requests in my app but only capture one of them by "httpscoop".

envir: Unity 4.7.2f

device: iphone5s

My app is already uploaded to appstore , and is ready for install.

I'm sure that the requests all succeed because if not the app will stop.

My code is below as simple:

new WWW("http://ift.tt/298EfYN");

This issue appears only on part of the ios device. It seems that the WWW request did not do http request but only return the cached data.When I delete the app and reinstall it , the issue would be fixed.So it's hard to rebuild the issue.

My question is , Is there some condition that WWW http request would not do the http request but only return the cached data?(I also checked the http server and did't receive the excepted requests) Or Give me some directions to figure it out.

Any help will be appreciative.