Why does the value of a mapping(bytes32 => uint8) seem to change between transaction calls?

The contract code:

pragma solidity ^0.4.10;

contract Test {
    mapping (bytes32 => uint8) private dict;

    function Test() {}

    function Set(bytes32 key, uint8 val) returns (uint8) {
        dict[key] = val;
        return dict[key];
    }

    function Get(bytes32 key) returns (uint8) {
        return dict[key];
    }

}

and I run on testrpc:

contract_file = 'test/test.sol'
contract_name = ':Test'

Solc = require('solc')
Web3 = require('web3')

web3 = new Web3(new Web3.providers.HttpProvider("http://localhost:8545"));
source_code = fs.readFileSync(contract_file).toString()

compiledContract = Solc.compile(source_code)
abi = compiledContract.contracts[contract_name].interface
bytecode = compiledContract.contracts[contract_name].bytecode;
ContractClass =  web3.eth.contract(JSON.parse(abi))

contract_init_data = {
    data: bytecode,
    from: web3.eth.accounts[0],
    gas: 1000000,
}

deployed_contract = ContractClass.new(contract_init_data)

deployed_contract.Set.call("akey", 5)
deployed_contract.Get.call("akey")

bizarrely, this is the output I get in the node terminal:

> deployed_contract.Set.call("akey", 5)
{ [String: '5'] s: 1, e: 0, c: [ 5 ] }
> deployed_contract.Get.call("akey")
{ [String: '0'] s: 1, e: 0, c: [ 0 ] }

This result is the outcome of a long debugging session... what is going on? It seems distinctly like something is broken here, but I followed a tutorial which did something very similar which seems to work...

also:

> Solc.version()
'0.4.11+commit.68ef5810.Emscripten.clang'