[horde] ob_gzhandler?

[Lars Hecking]

 I was having weird problems with some of the horde modules not working,
 but was able to sort them out by removing isWarning calls as per horde
 admin FAQ. However, one problem remains I have no solution for yet, and
 I don't even know which module is responsible:

PHP Warning:  (null)() [<a href='http://www.php.net/ref.outcontrol'>ref.outcontrol</a>]: output handler 'ob_gzhandler' cannot be used twice in Unknown on line 0
PHP Warning:  (null)() [<a href='http://www.php.net/ref.outcontrol'>ref.outcontrol</a>]: output handler 'ob_gzhandler' cannot be used twice in Unknown on line 0

 Ideas?