Don't panic.
roconnor has been experimenting with spending "duplicate coinbase transactions" on the testnet. Block explorer is confused, and isn't seeing the 50 bitcoins generated to that address in testnet block 45,442 (because the generation transaction has the same ID as the generation transaction in block 45,333).
Expect code changes before the 0.6 release is final to discourage and eventually prohibit accepting blocks with duplicate coinbase transactions; although we can't see a way to exploit this weirdness to cheat anybody (it is easy to cheat yourself out of bitcoins using duplicate coinbase transactions that cannot be spent), it's definitely not a good thing.
