Autocomplete combobox .net doesn't work

this should be a simple issue! :-)

In a Winform I have a combobox that is populated at runtime, from a textfile, using LINQ code.

The combo contains a list of countries.

I set DropDown style to "DropDown"

Autocompl开发者_开发知识库ete mode to SuggestAppend (or Suggest, it doesn't change the behavior for me) AutocompleteSource to ListItems

And when I run and enter some text in the form, NOTHING HAPPENS!

I must click the combo right arrow to see the list.

Any clue?