Do I have to type in the full customer's name on the invoice screen? Didn't there used to be a drop-down list?
But I'm glad to be able to deny your conclusion above: the system will search on any partial match, both on the customer number or on the customer name. So, there's no need to spell them quite exactly.
Also, if you want the drop downs back, there's a setting in the System -> Defaults screen (third item below the currency settings input box; "Max per dropdown"). If you enter 99999 into that (assuming you don't have that many customers), you'll be presented the selection list you're used to.