Huh! I had this happen recently -- puzzled the heck out of me too. The box in question has one Plextor and one LG. Push all the buttons you want, no eject but soft eject worked (to my amazement). If you hadn't mentioned it here I'd still be thinking I'd imagined the whole thing!
I checked all the cables, fiddled around some... drives back again. Had a brief spell of the 'sticky directory' issue. Shortly after that my power supply began refusing to boot the machine (Enermax 650w) followed by one of the hard-drives biting the bullet.
This little tale of woe doesn't help you a bit, I know. Just wondered if my combination of circumstances gives any clues. Haven't come to grips with it as I'm busy, so I just said some rude words and shifted to another system. There's no back-up quite as effective as a redundant system.
Hope you get it sorted!
[Edit -- can't spell, evidently can't proof-read until after posting *sigh*]