If I unlock an encrypted wallet for 359711509437336256 or less seconds, I can sign transactions with it:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336256
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
      "complete": true

But if I unlock it for 359711509437336257 or more seconds, it appears to have unlocked but I can't sign any transactions:

    $ bitcoin-cli walletpassphrase "$x" 359711509437336257
    $ echo $?
    0
    $ bitcoin-cli signrawtransaction $tx | grep complete
    error code: -13
    error message:
    Error: Please enter the wallet passphrase with walletpassphrase first.

I don't know the significance of that number. It's nowhere near a power of 2.

I was trying to unlock the wallet effectively "forever", so put a big number. If I use too big a number (2^63 or more) I get an error message `JSON integer out of range` but for numbers between 359711509437336257 and 2^63-1 inclusive I get no error, but no actual unlocking.
bool p2sh = true;
    if (!request.params[1].isNull()) {
        p2sh = request.params[1].get_bool();
    }
    Witnessifier w(pwallet);
    bool ret = boost::apply_visitor(w, dest);
    if (!ret) {
        throw JSONRPCError(RPC_WALLET_ERROR, "Public key or redeemscript not known to wallet, or the key is uncompressed");
    }
    CScript witprogram = GetScriptForDestination(w.result);
    if (p2sh) {
        w.result = CScriptID(witprogram);
    }
    if (w.already_witness) {
        if (!(dest == w.result)) {
            throw JSONRPCError(RPC_WALLET_ERROR, "Cannot convert between witness address types");
        }
    } else {
        pwallet->AddCScript(witprogram);
        pwallet->SetAddressBook(w.result, "", "receive");
    }
    return EncodeDestination(w.result);
}
struct tallyitem
{
    CAmount nAmount;
    int nConf;
    std::vector<uint256> txids;
    bool fIsWatchonly;
    tallyitem()