ob_start callback not fired with ob_get_clean()

I am wondering why the call to ob_get_clean and ob_get_contents does not trigger the callback function registered with ob_start('mycallback') I don't want to dump buffer to the browser but instead need to just store results in a variable, thus using ob_get_clean() but why it's my callback being executed during this call? It's actually in the documentation and ob_get_clean is not listed among the functions that trigger the callback. Is there a good reason why callback not fired for these functions? Dmitri Snytkine Web Developer Ultra Logistics, Inc. Phone: (888) 220-4640 x 2097 Fax: (888) 795-6642 E-Mail: dsnytkine@ultralogistics.com Web: www.ultralogistics.com "A Top 100 Logistics I.T. Provider in 2011"