MoodleFN

1: Yes I am referring to assignments
2: No this is not happening to all asignments. only to one course.
3: this course is created in Moodle 2.5
4: the default grading.
5: no, to bad. not even log level set to developer

I think this have to do with the combination plugin "Ajax Marking block". I try to reproduce the problem in another course.