I have a problem met an User Registration form, sometimes it creates 2 exactly the same users. I could nog reproduce the problem in any way. Clicking multipe times on the submit button had no effect. Also fast refreshing the page after submitting the form had no effect.
I inspected the plugin and i see that it is checking for existing usernames:
$user_id = username_exists($user_name);
See the following images for two exact the same users in our WordPress installation:
Do you have any idea what is causing this problem?
We are using the W3 Total Cache plugin for caching, could that cause some problems? The option "Database Cache" is enabled.