Correct.

Zapwallet removes ALL transactions from the wallet (confirmed, unconfirmed, sent, and received).

Then when you re-scan, the wallet finds all of the CONFIRMED transactions (both sent and received) in the blockchain.

The end result will be that your wallet should ONLY have CONFIRMED transactions and that the balance should reflect the total amount of confirmed transactions you received minus the total amount of confirmed transactions that you sent.

Note that it is possible for someone else to keep a copy of any unconfirmed transaction that you have ever broadcast to the network.  As long as that unconfirmed transaction is still valid, they could re-broadcast it without your permission.  Therefore, it is possible that, at some time after the re-scan, an old unconfirmed transaction could show up in your wallet again.