[horde] Problem with iPhone (iOS 7.1) and ActiveSync 2.15.1

[lst_hoe02 at kwsoft.de]

Tryed again today with ActiveSync 2.15.1. It first looks like working,  
but after a restart of the Phone the same behaviour is shown eg. the  
phone never finish to sync the mail account which has worked perfectly  
with ActiveSync 2.15.0. The only error in the debug log is as follow:

2014-05-19T16:50:25+02:00 INFO: [31184] Obtained synckey for  
collection @Calendar@ from cache:  
{537710f4-01b0-4379-b96f-369f55d64be0}14
2014-05-19T16:50:25+02:00 INFO: [31184] Collection added to collection  
handler: collection: @Calendar@, synckey:  
{537710f4-01b0-4379-b96f-369f55d64be0}14.
2014-05-19T16:50:25+02:00 DEBUG: [31184] I    <Ping:Folder>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     <Ping:ServerEntryId>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I       @Contacts@
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     </Ping:ServerEntryId>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     <Ping:FolderType>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I       Contacts
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     </Ping:FolderType>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I    </Ping:Folder>
2014-05-19T16:50:25+02:00 ERR: [31184] Attempting to add a collection
                     to the sync cache while requiring a synckey, but no
                     synckey could be found. Most likely a client error in
                     requesting a collection during PING before it has issued a
                     SYNC.
2014-05-19T16:50:25+02:00 DEBUG: [31184] I    <Ping:Folder>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     <Ping:ServerEntryId>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I       @Notes@
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     </Ping:ServerEntryId>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     <Ping:FolderType>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I       Notes
2014-05-19T16:50:25+02:00 DEBUG: [31184] I     </Ping:FolderType>
2014-05-19T16:50:25+02:00 DEBUG: [31184] I    </Ping:Folder>
2014-05-19T16:50:25+02:00 ERR: [31184] Attempting to add a collection
                     to the sync cache while requiring a synckey, but no
                     synckey could be found. Most likely a client error in
                     requesting a collection during PING before it has issued a
                     SYNC.

I can also send the whole log in private mail if it helps.

A revert to ActiveSync 2.15.0 immediatly cleared the problem. Our  
upgrade procedure is stop the webserver, do a pear upgrade, invoke  
horde-clear-cache and db-migrate and start the webserver again.

Any idea what is wrong?

Regards

Andreas