SAP IDM modifies system user to dialog user automatically

Hi Experts,

We are observing strange behavior that whenever a system / service user created by SAP IDM in ABAP is modified again through UI standard form , upon submission IDM updates the user to Dialog while it has been assured that user type remains the same which is B/S. I've checked the modify pass and found that user type attrib is passed into SecurityPolicy. Could anyone throw some light on this? and how to tackle ?

Regards

Rims