two identical XHR requests made close togeather are combined irrespective of method (i.e even POST which should never be cached) and cache control headers. jsfiddle demonstrating: (numbers should be different, as per latest chrome canary). http://jsfiddle.net/D5s5M/2/ Issue is now fixed in chromium (canary), still present in webkit: https://code.google.com/p/chromium/issues/detail?id=361087 this is very bad. i.e 'POST /api/getUUID' -> returns unique ID. If two of those calls happen close enough together the same ID will be returned to both. the logs will even show both requests going out, but if you watch a proxy you'd see only one request was actually made...