@1337jamie: I think the "slits" are scratches from sliding the phone open/closed. Mine hasn't had this happen yet, but I've heard complaints of them getting scratched or broken.
I had a case like that- it used magnets to keep the flap closed. I'd put my phone in with the keypad locked. (It's the SE W580 slider type) and 90% of the time when I'd take my phone out, it'd be unlocked.
I took the phone out, locked it & set it on top of the part containing the magnets. Sure enough, it triggered the buttons for the unlock sequence.
While what happened to me doesn't appear to have done any damage, I bought a magnet-free case anyway. Like Reiman said, not the best idea.
I've made a bunch of W580 themes and I don't notice a color change. Most of my themes have a corresponding light theme. Does the "Light Effect" preferences override the theme light settings?