There is a configuration variable called WIN_F4_DROPS_COMBOBOX
This configuration variable applies only to programs running under Windows.
Its default value is "1" (on, true, yes), so, combo boxes use the standard Windows handling for the key. Pressing while a combo box is active causes it to drop its drop-down list, and the COBOL program is not notified of an exception.
When this variable is set to "0" (off, false, no), pressing with a combo box active causes the COBOL program to get the exception, but the combo box does not drop its drop-down list.