I don't know if this has been mentioned here, but it seems that 4.2.1 made it more difficult to change your lock backgrounds with the native method when using themes? (I'm on 4.1, so can't test that out.) At any rate, I've been reading about people who, every time they want to change their wallpaper, need to SSH the new file into their theme.
If that's the case, you might try Wallpaper JPEGifier, a new tweak that makes it easier to replace your LS wallpaper on the go. If anyone on 4.2.1 is having that issue, let us know if this helps!
If that's the case, you might try Wallpaper JPEGifier, a new tweak that makes it easier to replace your LS wallpaper on the go. If anyone on 4.2.1 is having that issue, let us know if this helps!