invalid date recognition, irregular because of sorting template list (sometimes not reproducible by fail2ban-regex, cause will be not sorted)

date in following log line (from nginx) will be wrong detected:
2012/10/11 02:37:17 [error] 18434#0: *947 user "test" was not found in "/www/...", client: 192.168.1.5, ...

sometimes it is [correct] - 2012/10/11 (%Y/%m/%d) = 1349919861.71
sometimes it is [invalid] -   12/10/11 (%d/%m/%y) = 1349915838.06
and older as now - 1800 seconds (therefore will be not found)

solution: regular expression fixed, cause date in log used always after non symbol (\W) character, so r"\d{2}/\d{2}/\d{2}" will be r"(?<!\w)\d{2}/\d{2}/\d{2}".