Strange AUTO_INCREMENT behavior

I have a very strange problem with MySQL. I'm using an AUTO_INCREMENT column as the primary key in one of my tables. Data is inserted into the table from remote clients through a HTML form. The server-side app is PHP/FastCGI. The problem is that sometimes I get double entries into the table from one post. The AUTO_INCREMENT column increments correctly, but it duplicates the data and creates two rows in the table. This seems to only be occurring when the remote client is using a firewall. If the client turns off their firewall, the duplicate entries stop.

The AUTO_INCREMENT item is a bigint(18) unsigned. It functions as the primary key and is the only index in the table.

I've had this problem across several different versions of PHP and MySQL. Has anyone had a similar experience?

Thanks!

[Xnuiem]

I dont think this is a MySQL issue, but an application issue. I have seen this in some places before with an Image Gallery app a few months ago.