I see you do a commit with events. Do you do another commit in either the before or after commit action of task? Try temporarly setting the commit to 'without events' to check if the problem still occurs. If it does then it could be that you do a commit and a refresh action in the before/after commit. This has given me similar problems in the past.
This is not an easy one. I can only give some hints.
Check the created objects and see whether they are committed or rolled back. Maybe this created object is filled in as referenced object but not stored at the end.
This may happen over forms and sub-forms (a new, not committed, object is shown in a form). The form contains multiple next steps (read: buttons) in the workflow.
I remember fixing something in Mendix 4 where an object was unnecessarily retrieved after a rollback, but I don't know if this was already an issue in Mendix 3. Would it be possible for you to check if this still happens with a recent Mendix 4 version?