When you make a world in the snapshot, then open it in 1.7, you lose all your items

Downgrading is not supported since it is not intended, e.g. some of the latest snapshot's blocks are not available in 1.7.x.

Oliver is right. Downgrading from a snapshot world to 1.7 can cause it to be corrputed, causing you to lose your items, unless you have a backup installed.