I'm going to need to investigate this, because the text editor dialog should be using a fixed width/monospace font (it's using Consolas at the moment which is available on MacOS based on the quick search I did). So I have no idea why it's not using a monospace font on MacOS if that's what you are seeing. I generally would not recommend using tabs at all though - I would recommend using 4 spaces, because MobileSheets may not render tabs as you are expecting. You may also want to switch the font for lyrics to use a monospace font in MobileSheets if you rely on the spacing to be exact.
Mike
Mike