Hello Nadya.

Weird... How does code affect opening form and closing without changes? BTW, my colleague somehow found the same behavior in one of her forms. I suggested to do COMPILE FORM, but I don't know, if it helped or not...

Compiling the form will not help. When you set the ListIndex of a data bound Combo box, you are changing its value. Changing its value automatically changes the data in the field specified by its controlSource just like setting a text box's Value changes the value in the underlying data.