Need help with pokemon items in platinum.?

i gave my weavile a leichi berry to hold. i went into battle the elite 4 and then put it in the pc. when i took it out the berry was gone. the same thing happened again with my porygon-z. i was leveling up on the elite 4. porygon was holding the focus sash so it wouldnt get KO'd right away, but when i went in and fought the bug guy porygon died on first shot and when i checked to see if it was still there, it was gone! wtf!