undefined in callback list

Hi,
once in a while our agents have entries in their callback list where every field except the comments-field says "undefined". Because of the comments-field I could find out the lead_id and check the entries in vicidial_callbacks, vicidial_list and vicidial_log. Everything looks fine, no unusual data in these tables.
Does anyone have a clue what the problem could be?
Thanks,
heinz
once in a while our agents have entries in their callback list where every field except the comments-field says "undefined". Because of the comments-field I could find out the lead_id and check the entries in vicidial_callbacks, vicidial_list and vicidial_log. Everything looks fine, no unusual data in these tables.
Does anyone have a clue what the problem could be?
Thanks,
heinz