actually in proxy server it does not matter whether current session id is actually the id of the test which is running. global.currentSessionid is just an unified id used by proxy to identify each test session when running multiple test sessions. it could even be a random number or anything else, so if overwrite by other tests it would be OK since it does not have be the current session id.  And also this id is only useful when targeting page has multiple cross-domian iframes, otherwise it won't be used.