Changes have been made in Git (FRAMEWORK_5_2):

commit 06be1f07c6cb14e3a14a217aeb80f13c6506cb53
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Wed Oct 28 13:48:21 2015 -0400

     Bug: 14137 Return future and incomplete tasks.

     This is needed for recurring tasks to be returned after the initial
     instance has been completed.

  nag/lib/Api.php |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

http://github.com/horde/horde/commit/06be1f07c6cb14e3a14a217aeb80f13c6506cb53

Changes have been made in Git (master):

commit c3fcc852cd9cab0898aa5688f955ce64be1444e8
Author: Michael J Rubinsky <mrubinsk@horde.org>
Date:   Wed Oct 28 13:48:21 2015 -0400

     Bug: 14137 Return future and incomplete tasks.

     This is needed for recurring tasks to be returned after the initial
     instance has been completed.

  nag/lib/Api.php |    2 +-
  1 files changed, 1 insertions(+), 1 deletions(-)

http://github.com/horde/horde/commit/c3fcc852cd9cab0898aa5688f955ce64be1444e8

Given today is day J.
Create a task for target J+10, with a start date J-2. Set task 
recurrence to every 1 month on the same date.
Go to Agenda/kronolith. Ensure the tasks are shown.
The new task appears correctly in the agenda.

Now go back to the task list, and complete the task in the task list.

The outstanding task list no longer shows the task, as expected. The 
All tasks list or the future task list shows the task, with a target 
date of J+10D+1M, as expected.

Now go to the calendar/kronolith. Select a view of next month.

Expected behaviour: the task should appear in the calendar, as did the 
previous instance.
Observed behaviour: the task does not show on the next occurrence date.

For reference:
kronolith version used is 4.2.9