Every time someone (or something) GETs one of my web pages, I log the call from PHP. It's a simple SQL INSERT statement that saves a few values in $_SERVER[''] to MySQL.
Often there will appear two log entries for the same GET, within one second of each other. This does not happen consistently. Sometimes there are no duplicate records, very infrequently three records. I've verified that these are for the exactly identical values of $_SERVER['HTTP_REFERER'], and that these calls appear only once in the source code flow of logic.
Have any of these happened while you are testing, and can you duplicate it?
within one second of each other.
I watch people double-click all the time, for many users it's just how they navigate, never knowing a single click is required. This could account for part of it.
The second is just a "suspicion" of mine. I'm on satellite, and satellite is inherently a proxy server. My requests are sent to the proxy and routed through. Sometimes I suspect something gets hosed up in the routing and the proxy doesn't "know" if a request got through so it sends it again. I have no facts to verify this, but over the course of time I've experienced some oddities on some resources - for example, quite often on this site I get a double post and am not sure if this is an issue with the server here or my connection.