Sales/Purchases: Customer/Supplier selection dropdown box should be hidden after clicking arrow again

The drop down box down arrow only allows the drop down box to open and does not allow it to close.  If there is no change needed or I just wanted to see what the options are I then have to click Cancel within that box or click elsewhere on the screen to get rid of the drop down box. 

It is often the case that other types software allows the user to toggle a drop down box display on and off by simply reclicking the down arrow. 

Software is always easier to use if there is consistency across the different types.

"Clicking the drop down box down arrow should toggle the options"