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

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