Is the task still in your active task Window (Alt-Q) when you log back in ? I assume yes, since you say the players have to remove the task and then accept it again.
If the answer to the previous question is yes, does the activity progress register the hand-ins (i.e. go to 1/4, 2/4, 3/4, Done etc.)
Does the same bug happen if you zone rather than logout ?
Are there any errors in your logs relating to tasks (e.g. database updates failing) ?
Did it work fine under a previous version of the server ?
What version of the client (Titanium or SoF or both) does this problem happen with ?
EDIT:
I just tested this simple task:
Code:
INSERT INTO `tasks` (`id`, `duration`, `title`, `description`, `reward`, `rewardid`, `cashreward`, `xpreward`, `rewardmethod`, `startzone`, `minlevel`, `maxlevel`, `repeatable`)
VALUES (500, 0, 'Water Flasks', 'Give 4 water flasks to Guard Bixby in Qeynos Hills. Reward, a SSoY and 10 silver.', '', 5500, 10, 0, 0, 0, 0, 0, 1);
INSERT INTO `activities` (`taskid`, `activityid`, `step`, `activitytype`, `text1`, `text2`, `text3`, `goalid`, `goalmethod`, `goalcount`, `delivertonpc`, `zoneid`, `optional`)
VALUES (500, 0, 0, 1, '', '', '', 13006, 0, 4, 4063, 0, 0);
Using both Titanium and SoF. Each time I accepted the task, logged off, then logged back on and handed in the 4 water flasks and it worked fine.