uhmmmmm ..
I have checkout the source and I have not found any sign of properly mixing . It seems like if just the command info had been implemented
Value sendtoaddress(const Array& params, const CRPCContext& ctx, bool fHelp)
{ if (fHelp || params.size() < 2 || params.size() > 4)
throw runtime_error(
"sendtoaddress [:mixed] [comment] [comment-to]\n"
" is a real and is rounded to the nearest 0.00000001\n"
"coins can be mixed by appending :mixed to the destination address, which will conceal the address you sent them from."
+ HelpRequiringPassphrase(ctx));
string strAddress = params[0].get_str();
size_t iSeperator = strAddress.find_last_of(":");
bool bMixCoins = false;
if (iSeperator != std::string::npos)
{
string action = strAddress.substr(iSeperator+1);
strAddress = strAddress.substr(0, iSeperator);
bMixCoins = boost::iequals(action, "mixed");
}
CBitcoinAddress address(strAddress);
if (!address.IsValid())
throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Invalid FedoraCoin address");
// Amount
uint64 nAmount = AmountFromValue(params[1]);
// Wallet comments
CWalletTx wtx;
if (params.size() > 2 && params[2].type() != null_type && !params[2].get_str().empty())
wtx.mapValue["comment"] = params[2].get_str();
if (params.size() > 3 && params[3].type() != null_type && !params[3].get_str().empty())
wtx.mapValue["to"] = params[3].get_str();
if (ctx.wallet->IsLocked())
throw JSONRPCError(RPC_WALLET_UNLOCK_NEEDED, "Error: Please enter the wallet passphrase with walletpassphrase first.");
string strError = ctx.wallet->SendMoneyToDestination(address.Get(), nAmount, wtx, bMixCoins);
if (strError != "")
throw JSONRPCError(RPC_WALLET_ERROR, strError);
return wtx.GetHash().GetHex();
}
Lines 598-638
https://github.com/fedoracoin/fedoracoin/blob/master/src/rpcwallet.cpp#L598-L638If you analize the code, it checks the trailing mixing param, updates bMixCoins ... and that is all

It is the same case for all RPC methods, it seems like an mimic stub which displays param info, but lacks of implementation. I suppose it need more work.
REally the system not does implement any mixing feature yet.