Fix is working.

First I thought that the missing space in the explode function ("," 
instead of ", ") will cause troubles, but it works. Tags get 
concatenated in turba/lib/Object.php in function synchronizeTags() 
with a space. Maybe the tags get trimmed somewhere later or the sync 
client handles this...

Turba 4.2.1

Changes have been made in Git (FRAMEWORK_5_2):

commit 0d7d3252d31162fd5ce1adc16429047e4fe791d0
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Thu Jul 24 16:12:30 2014 -0400

     Bug: 13393  Fix exporting Tags/Categories in vCard.

  turba/lib/Driver.php |    8 ++++++--
  1 files changed, 6 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/0d7d3252d31162fd5ce1adc16429047e4fe791d0

Changes have been made in Git (master):

commit 50b18d67d8398e200e3ba78f1985b2760c4e9189
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Thu Jul 24 16:12:30 2014 -0400

     Bug: 13393  Fix exporting Tags/Categories in vCard.

  turba/lib/Driver.php |    8 ++++++--
  1 files changed, 6 insertions(+), 2 deletions(-)

http://github.com/horde/horde/commit/50b18d67d8398e200e3ba78f1985b2760c4e9189

Found out, that Turba only exports fields listet in the backend-map, 
where "__tags" is not listed for a mysql backend (see lib/Driver.php 
function tovCard()). When manually adding "__tags" to $attributes, it 
works. Either need to add "__tags" to the backend-map (question how?) 
or need to respect tags somehow in the tovcard-code.

My quick and dirty solution:
$attributes[] = '__tags';

Found another problem in turba/lib/Driver.php function tovCard(), when 
reading "__tags" and trying to set the vcard-attribute CATEGORIES, 
$val holds the tags as concattenated string (as retrieved by the 
Turba_Tagger in turba/lib/Object.php), but needs to be an array:

$vcard->setAttribute('CATEGORIES', null, array(), true, explode(', ', $val));

Wen synching contacts from a Samsung Galaxy S3, contact groups get 
correctly imported as tags in horde. When synching back from Horde, 
tags don't get exported.