The F4-key does not generate an exception with a Combo Box control.
Pressing <F4> while a combo box is active causes it to drop its drop-down list, and the COBOL program is not notified of an exception.
If the runtime configuration variable WIN_F4_DROPS_COMBOBOX is set to its default value of "1" (on, true, yes), then combo boxes use the standard Windows handling for the <F4> key.
When this variable is set to "0" (off, false, no), pressing <F4> with a combo box active causes the COBOL program to get the exception, but the combo box does not drop its drop-down list.
It is not possible to get both behaviors at the same time.
Incident Number: 2191737