A semi-opaque ribbon is observed in the main window:

![DeepinScreenshot_bitcoin-qt_20200119212040](https://user-images.githubusercontent.com/32963518/72686984-752bce80-3b02-11ea-8e54-a4d0e6448c1f.png)

![DeepinScreenshot_bitcoin-qt_20200119212253](https://user-images.githubusercontent.com/32963518/72686986-7a891900-3b02-11ea-87b8-cb2a7ff5b791.png)

Tab switching does not remove it. Window moving does not remove it.
It vanishes after window resizing.

**To reproduce**
Run with `-regtest`, generate some blocks (200 in my case), then quit.
Remove `rev00000.dat` file to trigger an error.
Run with `-regtest` and in the dialog "Do you want to rebuild the block database now?" click "OK".

**System information**
Linux Mint 19.3 + Cinnamon 4.4.8

Both versions affected:
- 0.19.0.1 (gitian)
- master + system Qt 5.9.7
ui->expectedTimeLeft->setText(GUIUtil::formatNiceTimeOffset(remainingMSecs / 1000.0));
        } else {
            ui->expectedTimeLeft->setText(QObject::tr("unknown"));
        }
        static const int MAX_SAMPLES = 5000;
        if (blockProcessTime.count() > MAX_SAMPLES) {
            blockProcessTime.remove(MAX_SAMPLES, blockProcessTime.count() - MAX_SAMPLES);
        }
    }
    
    ui->newestBlockDate->setText(blockDate.toString());
    
    ui->percentageProgress->setText(QString::number(nVerificationProgress*100, 'f', 2)+"%");
    ui->progressBar->setValue(nVerificationProgress*100);
    if (!bestHeaderDate.isValid())
        
        return;
    
    
    int estimateNumHeadersLeft = bestHeaderDate.secsTo(currentDate) / Params().GetConsensus().nPowTargetSpacing;
    bool hasBestHeader = bestHeaderHeight >= count;
    
    if (estimateNumHeadersLeft < HEADER_HEIGHT_DELTA_SYNC && hasBestHeader) {
        ui->numberOfBlocksLeft->setText(QString::number(bestHeaderHeight - count));
    } else {
        UpdateHeaderSyncLabel();
        ui->expectedTimeLeft->setText(tr("Unknown..."));
    }
}
void ModalOverlay::UpdateHeaderSyncLabel() {