Very annoying that we use both "HashTable" and "Hashtable" in various 
contexts.  That needs to be addressed at some point in the future.

Fixed.

Changes have been made in Git (master):

commit f01ae9ef912fe6732bc4a31b8dd9e8fba068ab0e
Author: Michael M Slusarz <slusarz@horde.org>
Date:   Mon Aug 25 11:47:22 2014 -0600

     Fix Bug #13507

  imp/lib/Factory/MailboxList.php |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

http://github.com/horde/horde/commit/f01ae9ef912fe6732bc4a31b8dd9e8fba068ab0e

I receive following error since recent update on git (last few days) 
when executing any search (i.e. unread messages in inbox).

Ein schwerer Fehler ist aufgetreten:
Class 'Horde_Cache_Storage_HashTable' not found

1. Horde_ErrorHandler::catchFatalError()

Details
Die vollständige Fehlermeldung wurde in Hordes Logdatei geschrieben 
und für Administratoren weiter unten ausgegeben. Benutzer, die keine 
Administratoren sind, bekommen diese Details nicht zu sehen.

ErrorException Object
(
     [message:protected] => Class 'Horde_Cache_Storage_HashTable' not found
     [string:Exception:private] =>
     [code:protected] => 0
     [file:protected] => /usr/share/horde/imp/lib/Factory/MailboxList.php
     [line:protected] => 126
     [trace:Exception:private] => Array
         (
             [0] => Array
                 (
                     [function] => catchFatalError
                     [class] => Horde_ErrorHandler
                     [type] => ::
                     [args] => Array
                         (
                         )

                 )

         )

     [previous:Exception:private] =>
     [severity:protected] => 1
     [logged] => 1
)



Hashtable Administration looks like this and I tried Clearing 
Hashtable and pulling complete new git installation:

Driver: Horde_HashTable_Memory

Does the backend provide persistent storage?: No

Does the backend provide locking support?: Yes

Backend Read/Write Test: Erfolg

Any ideas?