I am having the same problem, but my isn't a Mac. I do have the same graphics card as you idk if that has anything to do with it tho. If you find a solution I would be happy if you shared it with me. I do know though you can have a temp. fix by right clicking the icon on the far left and it will move the icons.
ps: that icon will become underneath the list of icons after you click it once. You can keep right clicking it till you find where you want the list of icon. After the first time you click it it will be alot smaller so you can easy know which one it is. This is only a temp fix it will change back each time you log in and out. So you can keep using this until you or anyone find a fix.