Echoes, prints, var dumps, etc.. always push to the output buffer. This is simply how PHP works. If you want to suppress the output then just use the ob (output buffer) functions, which is what they're designed to do. It is not practical to suppress an entire function, file, etc.. it should be suppressed on a use by use basis. Example as follows.
Code:
ob_start();
$avatar = $cbUser->getField( 'avatar', null, 'html', 'none', 'list' );
ob_end_clean();
Please see the PHP documentation below regarding this.
www.php.net/manual/en/ref.outcontrol.php
I've edited your subject and message to be more accurate and less damaging as it's absolutely false information and may mislead our less experienced userbase.