Fixed in Horde_Core.

Changes have been made in Git for this ticket:

[mms] Fix merging config data (Bug #10381).

  4 files changed, 184 insertions(+), 2 deletions(-)
http://git.horde.org/horde-git/-/commit/c9274cd01b407ed251d4a130943ef146e71278d1

Unfortunately, this is expected.  array_replace_recursive() does the 
following:

$a1 = array('a', 'b', 'c');
$a2 = array('d');

array_replace_recursive($a1, $a2) = array('d', 'b', 'c');

What we really want in this case is actually just: array('d').  In 
other words, we want the value of $conf['menu']['apps'] in imp to 
completely overwrite the value of $conf['menu']['apps'] from horde.   
This is because these arrays are nothing more than lists.  If an array 
is a list (as opposed to a hash map), it should be directly replaced.

However, PHP does not provide an API to determine if an array is 
currently a list or a hash map.  We could fake around it by doing 
something like checking if every key is a number and, if so, we would 
treat that array as a list and overwrite it with an applications list. 
  Or we have to specially treat the menu/apps config option within 
Horde_Registry.

Ah, I misread your initial comment. It about the duplicate, not the 
merging of both configuration settings.

Well, it is not the behaviour I would expect. Having turba twice in 
the menu, but no entry for ansel is a irritating for me as a user.

That's the expected behavior then.

Sorry, I forgot to mention that both these greps were done in the 
horde-base directory. So yes, one is on the turba config and the 
second on the horde config.

Are you sure you don't have that menu array in horde/config/conf.php 
instead of Turba?

Given the following setting in my configuration files:

# grep turba imp/config/conf.php
$conf['menu']['apps'] = array('turba');
# grep turba config/conf.php
$conf['menu']['apps'] = array('ansel', 'imp', 'kronolith', 'turba');

the resulting menu in the dynamic view of imp is like:
turba
imp
kronolith
turba