Eh, I spoke too soon. After I verified that my bitcoin client registered my coins, I:
1. deleted my wallet from "~/.bitcoin" (no data loss; my backup is still intact)
2. re-ran ./bitcoin-qt so that it would generate a new wallet
3. moved the new wallet.dat file to a backup
4. re-copied my origianl wallet from my backup into "~/.bitcoin"
5. ran ./bitcoin-qt
Bitcoin started and again displayed 0.00 BTC. So, I:
1. closed my bitcoin client
2. executed `./bitcoin-qt -rescan`
This successfully registered my coins agian.
Is this a bug? ...or is it normal behaviour to have to execute " -rescan" when switching wallet files?