Feedback from user jtara
I believe I found a bug in your system. I'll provide the code I typed if the screenshot isn't clear enough.
URL from: http://www.checkio.org/mission/most-wanted-letter/solve/
HTTP_USER_AGENT: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36
URL from: http://www.checkio.org/mission/most-wanted-letter/solve/
HTTP_USER_AGENT: Mozilla/5.0 (Windows NT 6.3; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/35.0.1916.153 Safari/537.36