Since the beginning of the project, using the Preferences dialog box to control application font settings, there's been a bug in the repainting of TTntListView column headers, which afflicts the main window of the app. This might just be a bug in some graphics drivers, though; it doesn't show up on some other machines. What happens is that when a font is larger than the default, the original lower border of the column headers is left painted, obscuring part of the text. This works around it:

if LV.ShowColumnHeaders then
  begin
    LV.ShowColumnHeaders := False;
    LV.Invalidate;
    Application.ProcessMessages;
    LV.ShowColumnHeaders := True;
    LV.Invalidate;
    Application.ProcessMessages;
  end;

I've been trying to find a fix for this for a couple of years.