Repeated contract addresses when creating contract via JSON-RPC

[tinybike]

I'm attempting to load several different contracts onto the blockchain using eth_sendTransaction over JSON-RPC. I am encountering an unusual problem -- the contracts appear to be broadcast successfully, but the address in the result field is always the same! Here's an example:

jack@vent:~/src$ curl --data '{"jsonrpc":"2.0","method":"eth_sendTransaction","params":[{"from":"0x63524e3fe4791aefce1e932bbfb3fdf375bfad89","data":"0x603980600b6000396044567c01000000000000000000000000000000000000000000000000000000006000350463643ceff9811415603757600a60405260206040f35b505b6000f3","gas":10000000}],"id":1}' http://127.0.0.1:8545
{
    "id": 1,
    "jsonrpc": "2.0",
    "result": "0x13aad6f5573db896e589d2fdef22da8c5033141d"
}

This particular contract is a very simple Serpent contract:

def ten():
    return(10)

The exact same address 0x13aad6f5573db896e589d2fdef22da8c5033141d is returned no matter what the contract I broadcast is.

When I restart geth, sending contracts works again (for a little while). After a bit of testing, it seems like the following error is triggering this behavior:

"error": {
    "code": -32603,
    "message": "Known transaction (c6a8cdc5)"
}

This error appears sometimes (but not always) when re-submitting a contract, which I'm assuming is a bug. For some reason, this error is followed by the unusual problem described above.

I'm running geth v0.9.9 on Ubuntu 14.04 (installed via ppa):

jack@vent:~/src$ geth version
Welcome to the FRONTIER
Geth
Version: 0.9.9
Protocol Version: 60
Network Id: 0
GO: go1.4.2
OS: linux
GOPATH=/home/jack/src/gocode
GOROOT=/usr/lib/go

[obscuren]

Thanks. Confirmed and working on a fix.