I have some panels that are sometimes oriented vertically and sometimes horizontally. When they're vertical, the title's on top with two square buttons [ - ] windowshade and [ x ] close. The title bar is also a handle for dragging to relocate it. When its horizontal, the whole title bar is rotated 90 degrees, but the content remains upside right and sometimes has to rearrange. This includes the text. The [ x ] button looks the same rotated 90, but I don't know what to do with the windowshade button. Do I flip it or not?
To avoid discussion type answers, I need justifications grounded in examples or precedent. For example, "The minus sign was originally intended to be a depiction of what the titlebar looks like when its shaded, so flip it" or "A button like [ | ] has a different meaning so its best to keep it horizontal" or "insert program name does it this way, so you should too"