从不同服务器调用时,file_get_contents返回不同的结果

I'm running a simple piece of php code, like so:

echo file_get_contents( 'http://example.com/service?params' );

When I run the code on my local machine (at work) or from my shared hosting account, or if I simply open the URL in my browser, I get the following result:

{"instances":[{"timestamp":"2014-02-28 18:03:39.0","ids":[{"id":"525125875"}],"cId":179,"cInstanceId":9264183220}]}

However, when I run the exact same code on either of two different web severs at my workplace, I get the following slightly different result:

{"instances":[{"timestamp":"2014-02-28 18:03:39.0","ids":[{"id":"632572147"}],"cId":179,"cInstanceId":4302001980}]}

Notice how a couple of the numbers are different, and that's all. Unfortunately, these different numbers are the wrong numbers. The result should be identical to the first one.

The server I'm making the call to is external to my workplace.

I've tried altering the file_get_contents call to include headers and masquerade as a browser, but nothing seems to give a different result (well, other than an error due to an accidentally malformed request). I can't use cURL because it's not installed on the servers where this code needs to be deployed.

Any clue what could be causing the differing results? Perhaps something in the request headers? Although I'm not sure why something in the headers would cause the service to return different data.

thanks.


(edit)

The service URL I'm testing with is:

http://iswa.ccmc.gsfc.nasa.gov/IswaSystemWebApp/CygnetLastNInstancesServlet?lastN=1&cygnetId=179&endTimestamp=2014-02-28+21%3A35%3A48

The response it gives is a bit different than what I posted above; I simplified and shortened the responses in my SO post to make it easier to read--but the essential information given, and the differences, are still the same.

I give the service a timestamp, the number of images I want to fetch which were created prior to that timestamp, and a 'cygnetId', which defines what sort of data I want the images to show (solar wind velocity, radiation belt intensity, etc). The service then echoes back some of the information I gave it, as well as URL segments for the images I requested.

With the returned data, I can build the URL for an image. Here's the URL for an image built from a "correct" response:

http://iswa.ccmc.gsfc.nasa.gov/IswaSystemWebApp/StreamByDataIdServlet?allDataId=525125875

Here's the URL for an image built from a "wrong" response:

http://iswa.ccmc.gsfc.nasa.gov/IswaSystemWebApp/StreamByDataIdServlet?allDataId=632572147

If you click the links above, you'll see that the "wrong" URL does not open an image--the response is blank.