MetaMask account balance not updating

Question

I've gone through with the debugger to make sure msg.sender is my metamask account and that it should be updating.

I'm messing with the 0xBitcoin ERC20 contract.

function myfunction() {
     balances[msg.sender] = balances[msg.sender].add(reward_amount)
     // My contract is 18 decimals but even after converting the amount to "ether"-like
     // units the amount is still 2 digits long. So it's not that the update is too small

     emit Mint(msg.sender, reward_amount, epochCount, challengeNumber
}

Where Mint is defined as

event Mint(address indexed from, uint reward_amount, uint epochCount, bytes32 newChallengeNumber);

So in summary my account balance doesn't update and I've checked

1) message.sender value

2) reward_amount is large enough that it should be visible

3) the transaction is going to completion without any errors preventing it

What could be going wrong that I haven't considered?

---

Here's the entire function. It's basically straight from the 0xBitcoin contract cited above.

function Mint(uint256 nonce, bytes32 challenge_digest) public returns (bool success) {
        bytes32 digest = keccak256(abi.encodePacked(challengeNumber, msg.sender, nonce));

        if (digest != challenge_digest) revert();

        if(uint256(digest) > miningTarget) revert();

        bytes32 solution = solutionForChallenge[challengeNumber];
        solutionForChallenge[challengeNumber] = digest;

        if(solution != 0x0) revert(); // same answer can't be awarded twice

        uint reward_amount = getMiningReward();

        balances[msg.sender] = balances[msg.sender].add(reward_amount);
        tokensMinted = tokensMinted.add(reward_amount);

        lastRewardTo = msg.sender;
        lastRewardAmount = reward_amount;
        lastRewardEthBlockNumber = block.number;

        _startNewMiningEpoch();

        emit Mint(msg.sender, reward_amount, epochCount, challengeNumber);

        return true;
    }

Answer 1

A reason for wallets to not notice new tokens being minted is that they will only listen for Transfer event.

In the ERC20 specification only Transfer event is defined.

For example OpenZeppelin's implementation generates a Transfer with sender being the null address 0x00000000...00.

emit Transfer(address(0), account, amount);