PHP CLI slow to exit with CURL + MySQL extensions

Description:
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OK, this is a strange one. If you have CURL and either the php_mysql or php_pdo_mysql extensions active, then PHP (command line) will hang for about 5 seconds before actually exiting the script.

This is especially problematic in a CGI scenario, because the connection to the browser isn't closed during this delay and it looks like the request isn't complete.

The problem goes away if I comment out the Mysql extensions in my ini file.