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
if (ev->type() == QEvent::ParentAboutToChange) {
        if (parent()) parent()->removeEventFilter(this);
    }
    else if (ev->type() == QEvent::ParentChange) {
        if (parent()) {
            parent()->installEventFilter(this);
            raise();
        }
    }
    return QWidget::event(ev);
}
void ModalOverlay::setKnownBestHeight(int count, const QDateTime& blockDate)
{
    if (count > bestHeaderHeight) {
        bestHeaderHeight = count;
        bestHeaderDate = blockDate;
        UpdateHeaderSyncLabel();
    }
}
void ModalOverlay::tipUpdate(int count, const QDateTime& blockDate, double nVerificationProgress)