Why is my wired keyboard's Eject key no longer working after OS upgrade?

Question

Though it sounds like a duplicate of this question, it isn't; the difference is that my eject key works when I connect it to another Mac, so the hardware is good.

The situation is that I have a MacPro3,1 tower with an optical drive that I recently upgraded to El Capitan. The eject key always worked before, but after the move to El Capitan it no longer works and I either have to use the menu bar command or press the physical button on the drive (it is an aftermarket BD-ROM from MacSales).

The keyboard is directly connected to the Mac, no USB hubs or anything in the middle. I have not changed any settings for Fn keys. I do have Karabiner installed to re-map the right-option key for Citrix sessions, but using its "display all keyboard events" tool, it seems that the eject key has no event associated with it. I would have thought this meant it is a hardware issue, but seeing how it worked with no problem on my other Mac, I'm guessing the key isn't mapped like the rest.

Any ideas?

Answer 1

In response to Allan's comments on the original question, I attempted safe mode and found that the eject key still worked and also realized that it worked before I logged in to my account. Obviously, it was something my profile was loading at login time.

While I'm not sure which item specifically helped, I did notice that I had an older "iTunes Helper" and also quitting iTunes (which is normally loaded all the time) did seem to correspond with the eject key working again, but I'm not 100% convinced that it was the precise culprit. While iTunes has always had a helper, I think this particular one might have been an artifact of an older installation that got carried over in the upgrade and caused the problem.