Changes have been made in Git for this ticket:

Bug #9975: Fix error message thrown while viewing message in virtual 
folder in traditional mode

  1 files changed, 3 insertions(+), 1 deletions(-)
http://git.horde.org/horde-git/-/commit/1a8517bab1e7623cd092af52c1d77bf18cb685c5

Changes have been made in Git for this ticket:

Fix constant name (Bug #9975).

  1 files changed, 1 insertions(+), 1 deletions(-)
http://git.horde.org/horde-git/-/commit/a2b236d089428704b03b29aa11ce1ce806674cae

I'm getting the following error instead:

Fatal error: Undefined class constant 'READERROR' in 
/home/jan/horde-git/imp/lib/Imap.php on line 403
Call Stack
#        Time        Memory        Function        Location
1        0,0058        1193616        {main}( )        ../message.php:0
2        1,3356        56395744        IMP_Flags->getList( array ('imap' => TRUE, 'mailbox' 
=> class IMP_Mailbox { protected $_cache = array (); protected $_mbox 
= 'impsearch00vinbox' }) )        ../message.php:461
3        1,3357        56397520        IMP_Imap->openMailbox( class IMP_Mailbox { protected 
$_cache = array (); protected $_mbox = 'impsearch00vinbox' }, 2 
)        ../Flags.php:126
4        1,3357        56398152        IMP_Imap->__call( 'openMailbox', array (0 => class 
IMP_Mailbox { protected $_cache = array (); protected $_mbox = 
'impsearch00vinbox' }, 1 => 2) )

the problem is from my piont of view the generated link to the message 
in the virtual inbox folder
example:
generated and not working:
https://xxx/imp/message.php?mailbox=impsearch%00vinbox&uid=30&thismailbox=Backup%2FDVBAG
manually changed and working:
https://horde.bigmichi1.de/imp/message.php?mailbox=impsearch%00vinbox&uid=30&mailbox=Backup%2FDVBAG

i tested only in my browser not changed any line of code

in my virtual folder list i can not open messages that are not in the 
inbox folder, when trying to open such a message i am redirected to 
the inbox folder with the error message "message not found"