Combobox settings that allow user entered value

There must be a setting that allows me to enter my own text into a combobox control that updates the value of the control and will save to the database. If I don’t set the drop down style, it allows me to edit the text in the field but it doesn’t keep in memory and on leave it wipes whatever I typed. There must be a way to allow a user to write a custom value like a text field to a combobox.

There’s an “Allow Custom” checkbox in the settings.