Using Linux, add a standard TEdit on a Form and fill the OnKeyPress with the following code:
procedure TForm1.Edit1KeyPress(Sender: TObject; var Key: char);
begin
if key=chr(13) then form1.Caption:=form1.Caption+'>';
end;
The above event is triggered when the project is running Linux using default gtk2 LCLWidgetType.
Now go to "Project/Project options..." menu, "Additions and Overrides", set the LCLWidgetType value to "customdrawn". Run the project again and you might see that the key press event is not triggered at all. I've looked at OnUTF8KeyPress event and this one is triggered for both gtk2 and customdrawn. Gtk2 triggers OnUTF8KeyPress before OnKeyPress, customdrawn triggers OnUTF8KeyPress and doesn't trigger OnKeyPress at all.
Maybe it's a bug.