problem with last changed on field in SU01

Hi gurus

Does anyone of you know what is the reason for this. I have added several new roles for user but the last changed on field does not update. My user ID should be shown there and the time I saved the changes. I can see the changes in the change documents but not in the field. I have earlier seen the changes i have done in that field.

Hope you could clarify me.

-Jaakko