When I click on the calendar or the down arrow, the calendar window opens and the mouse pointer remains focused on the calendar icon. If I just move the cursor down into the calendar window I can set the date without any problem. However, if the mouse pointer goes outside the calendar window, it does close the window. Only I these circumstances does the calendar window close before I can set a date. The problem is more likely to occur if I am using a touchpad (I hate touchpads!) as it is not as easy to control the mouse pointer movement. Is this what is causing your problem?