VFP ignores readonly property of combobox control if its style is 2 – Drop-down List.

I tried to fix this by adding a property readonlyemu and using the following code in the combobox interactivechange event:

IF this.readonlyemu
nodefault
return
endif

However, this allows user to change value from keyboard or
select other value from list. New value appears in the combobox.

How to prevent entering new values ?
Which is the best way to mark list box read only from VFP code ?