From some time we're noticing that several of our orders has been duplicated in Magento.
After investigation it turns out that all of the duplicated order was placed using IE11, and the requests were doubled. One request was made with 103 HTTP response code, and second with correct 302. Below is the example of doubled request taken from apache access logs:
93.*.*.* - - [14/Aug/2015:13:50:04 +0100] "POST /store/onestepcheckout/ HTTP/1.1" 103 145 "/; "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.0; Trident/5.0)"
93.*.*.* - - [14/Aug/2015:13:50:04 +0100] "POST /store/onestepcheckout/ HTTP/1.1" 302 30306 "; "Mozilla/5.0 (compatible; MSIE 9.0; Windows NT 6.0; Trident/5.0)"
That could suggest that IE and it's resending post request is the cause of the problems and we applied some hotfix to phtml files in order to prevent that. However that doesn't explain why those duplicated orders started to show just couple of weeks ago and were not showing before.
We checked our logs, and nothing explains that change in behaviour.
Did anyone noticed similar behaviour in your stores, and how did you fixed that?
Magento CE v. 1.7.0.2 with Idev Onestepcheckout module