[TYPO3-english] output handler 'ob_gzhandler' conflicts with 'zlib output compression'

[Robert Wildling]

I keep getting this warning in the backend:

PHP Warning: ob_start(): output handler 'ob_gzhandler' conflicts with 
'zlib output compression' in 
/[...]/typo3/sysext/core/Classes/Core/Bootstrap.php line 1006

I use:
TYPO3 CMS 6.1.1
MAMP 2
php 5.4.4 (with and without XCache or APC)

Any ideas, why this is?