Covet doesn't steal the foe's item...I don't know if thief does...
Ps2: so far in version 0.32 breeding didn't work with: Pikachu, Ralts, Exeggcute, Larvesta, Growlithe, Psyduck, Ursaring (I'm only in Ecruteak so I still have a lot to check)
PS4: Facing a Scyther with a Lucario freezes the game (also in version O.32)..and I have no idea why...maybe they can sense I have rock tomb on my Lucario...XD