Customer list under Quick Job Creation not updating


Recently the customer list in the drop down list under the Quick job creation button has stopped updating. A few customers were removed from the list, and then the list remained constant. Even customers for which I have entered a 5-6 jobs in the last 2 weeks have not been added. In the past the list used to update constantly according to the most common customer, but now – I don't remember exactly when this behaviour started – it is constant. Can this be fixed?