不同的AJAX XML来自使用JQuery的相同POST文件的相同PHP文件

I'm using the JQuery .ajax method to get the results of a simple PHP query in XML (which I've done various times within this project without a problem). However, the XML result that I receive from within my main project is different to what I expect (as tested by simply viewing the PHP file) when viewing the results in Firebug's console. I also tested this again by creating a new PHP file whose sole function is to run the ajax call and the results are correct, as expected.I'm using the JQuery .ajax method to get the re