As the subject says. ST:TNG is the only skin where this happens, since it shares the same line for both things. And you can see the "remains" of the message in the space between each button. Maybe I'm wrong, but I shouldn't be forced to stop calling SetButtons if there's a message active (at least if I repeatedly[*] call SetButtons after calling SetMessage it works fine with every other skin).
[*] I change the help at each screen refresh based on the menu selection, while I only need to show a message from time to time.
Bye