Ophaned block on etc chain
### Description

Ophaned block on etc chain


### Steps to Reproduce

1. set config.json like this  :

 "pools": [{
        "id": "etc1",
        "enabled": true,
        "coin": "ethereum-classic",
        "address": "0x196e38e38cbc70f2098b33c40e3e026ccfbff6ae",
        "rewardRecipients": [{
                "type": "op",
                "address": "0x196e38e38cbc70f2098b33c40e3e026ccfbff6ae",
                "percentage": 0.5
        }],
        "blockRefreshInterval": 500,
        "clientConnectionTimeout": 600,
        "banning": {
            "enabled": true,
            "time": 600,
            "invalidPercent": 50,
            "checkThreshold": 50
        },
        "ports": {
            "3072": {
                "listenAddress": "0.0.0.0",
                "difficulty": 1,
                "varDiff": {
                    "minDiff": 1,
                    "maxDiff": null,
                    "targetTime": 15,
                    "retargetTime": 90,
                    "variancePercent": 30
                }
            },
            "3073": {
                 "listenAddress": "0.0.0.0",
                 "difficulty": 5000
            }
        },
        "daemons": [
            {
                "host": "x.x.x.x",
                "port": 8545,
                "user": "",
                "password": ""
            }
        ],
        "paymentProcessing": {
            "enabled": true,
            "minimumPayment": 0.1,
            "minimumPaymentToPaymentId": 4.0,
            "payoutScheme": "PPLNS",
            "payoutSchemeConfig": {
                "factor": 2.0
            },
            "coinbasePassword": "",
            "keepUncles": false,
            "keepTransactionFees": true
        }

2.   start parity like this : 


./parity --chain classic --jsonrpc-interface=x.x.x.x --unlock 0x196e38e38cbc70f2098b33c40e3e026ccfbff6ae --password xxx --author 0x196e38e38cbc70f2098b33c40e3e026ccfbff6ae

3.   start pool  

then no error, everything work fines, stats and pplns payout manager

4.  start mining 

all share are accepted and works fine

5. found block

### Expected behavior

confirm block

### Actual behavior

all block are orphaned with the same block number

Wed Mar 04 2020 19:34:57 GMT+0100 (heure normale d’Europe centrale) | 9915971 | 18% | orphaned | 0 | 100%
-- | -- | -- | -- | -- | --
Wed Mar 04 2020 16:24:34 GMT+0100 (heure normale d’Europe centrale) | 9915971 | 44% | orphaned | 0 | 100%


### Reproduces how often

Allways

### Version

Parity Ethereum v2.7.2-stable   own build

miningcore master branch build with no error

ubuntu server 18.04

MiningcoreWeb.ui


### Additional Information



