Changes have been made in Git for this ticket:

[jan] Always use negative lookbehind assertions to work around bug in 
PCRE 6.6 (Steve Teti, Bug #10294).

  4 files changed, 46 insertions(+), 9 deletions(-)
http://git.horde.org/horde-git/-/commit/981d58b8b4cfb1c128fc48dcdab1aacc4737fbdf

Upon further investigation, it appears that this may be a bug in my 
version of PCRE.

http://bugs.exim.org/show_bug.cgi?id=559

Fixed in PCRE 6.7, but CentOS 5 is using PCRE 6.6.

On a Fedora Core 14 box running PHP 5.3.5 and PCRE 8.10, the positive 
lookbehind assertion works correctly.

Nevertheless, this patch gets this function working in CentOS, which 
may be valuable.

Patch for framework/Ldap/lib/Horde/Ldap/Util.php

While working with calendar permissions in Kronolith, I found that 
once I set permissions on a calendar for a particular group, the group 
disappeared from the permissions window, although the permissions 
seemed to work correctly.  I found the following errors in the horde 
log:

HORDE [kronolith] PHP ERROR: preg_split(): Compilation failed: 
lookbehind assertion is not fixed length at offset 9 [pid 24322 on 
line 292 of "/usr/share/pear/Horde/Ldap/Util.php

It appears that my version of PHP does not like the formatting of that 
regex.  There were three instances of a regex like this used in 
preg_split:

/(?<=[^\\\\]),/

It appears to me that the purpose of this regex is to split the string 
on commas, as long as the comma is not escaped by a preceding 
backslash.  I changed the three instances of this regex to a negative 
lookbehind assertion, which my version of PHP seems to like better:

/(?<!\\\\),/

I see other instances of this type of negative lookbehind assertion in 
Util.php, and it seems to be working on my setup.  I will attach a 
patch to Util.php in a subsequent post.

My server config:
CentOS 5.6 x86_64
Apache 2.2.3 installed via yum
PHP 5.3.3 installed via yum
PCRE 6.6 installed via yum