Hi,
waitbar itself doesn’t accept an 'Interpreter' name-value pair. Instead, create the bar, grab the text object MATLAB puts inside it, and set that object’s Interpreter to 'none'.
% Create the bar (R2014b or newer)
wb = waitbar(0,'My_waitbar_string_with_underscores');
wb.Children.Title.Interpreter = 'none';
If the bar has extra children (for example when you add a Cancel button) you may need to address the correct child explicitly:
wb.Children(2).Title.Interpreter = 'none'; % when a Cancel button exists
Another way to do is:
set(findall(wb,'Type','text'),'Interpreter','none');
Hope this helps!
