Listbox blinks when I click combobox

[projecttoday]

When I click on the combobox on my subform the listbox on the main form blinks. The table on which the combobox is based is part of the listbox's query and I guess this is the reason why. I could copy this table but is there an easier way to get rid of this blinking?

 

[projecttoday]

I am not requerying the listbox. The data are displayed in the listbox to inform the customer what the sales category is and the data are displayed in the subform because that's where the field is entered into the service code.