Automatic change in display?

Hi,

I have PI processbook, and there is display file which display different tag values. My Display also contains combobox which updates in display.open event. I also have tooltips and values updating constantly. My question is, whenever my display opens it marks a *(meaning that display file has been updated and need to be saved) though I didn change anything in code or display. So when I close it asks be to save the changes, though I didn changed. Why it could be? and how it can solved at a user level?

Thanks