[imp] HORDE PHP ERROR: array_keys() expects parameter 1 to be array, boolean given

[lists at jean-richard.ch]

Hello,

Since updating to imp 6.1.3 (and Hore 5.1.3, please ignore the folder name
"horde4" in the following log messages) I have the following issue with my
Horde installation:

1. The first login on a new browser (all cookies deleted, no previous
session active) works without any problems. In the log I can see the
following lines:

2013-08-27T21:39:38+02:00 NOTICE: HORDE [horde] Login success for <user>
[<ip>] to horde. [pid 31743 on line 161 of
"/data/wwwroot/ssl/horde4/login.php"]
2013-08-27T21:39:39+02:00 NOTICE: HORDE [imp] Login success for <user>
(Horde user <user>) [<ip>] to {localhost:143 [imap]} [pid 31743 on line 157
of "/data/wwwroot/ssl/horde4/imp/lib/Auth.php"]

2. if I logout and then login again I get the message "Error: Mail is not
activated. " in the web frontend and in the logfile I see the following
messages:

2013-08-27T21:40:48+02:00 ERR: HORDE [imp] Server does not support TLS
connections. [pid 31815 on line 94 of
"/data/wwwroot/ssl/horde4/imp/lib/Imap/Exception.php"]
2013-08-27T21:40:58+02:00 NOTICE: HORDE [horde] User <user> [<ip>] logged
out of Horde [pid 2089 on line 113 of "/data/wwwroot/ssl/horde4/login.php"]
2013-08-27T21:41:05+02:00 NOTICE: HORDE [horde] Login success for <user>
[<ip>] to horde. [pid 31870 on line 161 of
"/data/wwwroot/ssl/horde4/login.php"]
2013-08-27T21:41:09+02:00 WARN: HORDE [imp] PHP ERROR: array_keys() expects
parameter 1 to be array, boolean given [pid 31870 on line 433 of
"/usr/share/php/Horde/Imap/Client/Socket.php"]
2013-08-27T21:41:09+02:00 WARN: HORDE [imp] PHP ERROR: array_merge():
Argument #2 is not an array [pid 31870 on line 433 of
"/usr/share/php/Horde/Imap/Client/Socket.php"]
2013-08-27T21:41:17+02:00 ERR: HORDE [imp] Authentication failed. [pid 31870
on line 94 of "/data/wwwroot/ssl/horde4/imp/lib/Imap/Exception.php"]
2013-08-27T21:41:32+02:00 ERR: HORDE [imp] Authentication failed. [pid 31870
on line 94 of "/data/wwwroot/ssl/horde4/imp/lib/Imap/Exception.php"]

Does anybody know what I am doing wrong? 

- I use PHP 5.4.9 and dovecot as a mail server.
- When I delete the cookies I can login again (just once though)

Thanks for your help!
Best regards
Meinrad