When does php's mysql_pconnect consider a connection to be "available"?

Question

I'm using php-fpm (a fastcgi php manager) and am confused about when php would consider a persistent connection created with mysql_pconnect to be available instead of creating a new one.

Whenever I try enabling mysql_pconnect vs mysql_connect my open connections to my mysql server just climbs until I hit my max allowed. Without mysql_pconnect I have in the range of 30-50 mysql connections open at a time. My mysql wait_timeout is set at 5.

It feels like when I start using mysql_pconnect it just keeps creating NEW connections and not recognizing any of the old ones as available. Could php-fpm (or fastcgi) be causing this?

Are there any details about how mysql_pconnect considers a connection to be "available"?

Thanks.