[horde] No directory listing in IMP with PHP 7

[Twilek]

Hi,

I am trying to change to PHP 7 for some time now but there is one  
problem with horde which keeps me from doing it. I had this problem  
from the start and at first thought that it might have been an early  
bug of PHP 7.0. But with 7.1 approaching and 7.0 being regarded as  
stable things have not changed.
I am using a horde webmail installation with the latest pear beta  
packages (horde 5.2.16) and dovecot 2.2.25. I am using the IMAP  
backend of dovecot for authentication with horde. When using libmodphp  
5.6.22 with the latest apache 2 things work great. When switching to  
the latest php 7.0 all other Webapps that I am running work (so I  
guess libmodphp 7 works). Only horde works only partly. It lets my  
admin user authenticate normally. I see the dashboard and can access  
imp (and all other horde apps). There I see my inbox (via IMAP) with  
all mails and can read the mails. It does not read the the IMAP  
folders and the folder options in IMP cannot be opened. There are no  
errors in the horde log or in the dovecot log. Switching back to php 5  
fixes that problem. Another problem is that all users except my admin  
one cannot login. Horde log just shows "user xxx failed to login". As  
far as I can see there is something wrong with the IMAP communication  
(althought not everything is wrong as my admin user can login and can  
read mails in the inbox). As there are no telling error messages in  
the horde or dovecot log I am completely at a loss where to start  
looking. 

Regards

Henning