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
}
class ModalOverlay : public QWidget
{
    Q_OBJECT
public:
    explicit ModalOverlay(bool enable_wallet, QWidget *parent);
    ~ModalOverlay();
public Q_SLOTS:
    void tipUpdate(int count, const QDateTime& blockDate, double nVerificationProgress);
    void setKnownBestHeight(int count, const QDateTime& blockDate);
    void toggleVisibility();
    
    void showHide(bool hide = false, bool userRequested = false);
    void closeClicked();
    bool isLayerVisible() const { return layerIsVisible; }
protected:
    bool eventFilter(QObject * obj, QEvent * ev) override;
    bool event(QEvent* ev) override;
private:
    Ui::ModalOverlay *ui;
    int bestHeaderHeight; 
    QDateTime bestHeaderDate;
    QVector<QPair<qint64, double> > blockProcessTime;
    bool layerIsVisible;
    bool userClosed;
    void UpdateHeaderSyncLabel();
};
#endif