I don't have access to a display right now to check it but I think it does work but in a different way to what you're expecting. When printing text Invert mode only affects the foreground parts of the text, not the background. So for instance if you were to draw a filled rectangle, and then print some text on top of it in invert mode, the text will be drawn in the background colour - if that makes sense!I was hoping to invert a character but I can't get the DrawMode function to invert. It's not a mission critical requirement, just a nice to have, so if the functionality is broken, don't spend time fixing it on my behalf.
How difficult would it be to scroll a line of text? Looking at the library it looks tricky, but do able.
You could actually use the invert mode to do that in the same way as the Things example sketch does it. I'll grab a display when I'm in the office tomorrow and have a closer look.