Noticed this while reviewing #13529, but it's also in master @ 5ba77df. On macOS 10.13.6:

<img width="209" alt="schermafbeelding 2018-08-01 om 16 22 09" src="https://user-images.githubusercontent.com/10217/43527498-0f571db4-95a7-11e8-8d90-7863947a7689.png">


<img width="178" alt="schermafbeelding 2018-08-01 om 16 12 51" src="https://user-images.githubusercontent.com/10217/43526994-c9a515ec-95a5-11e8-96b8-9e2513e9aac5.png">

* `Show` in the action menu doesn't work if the app was hidden by `Command + H`, it does work when hidden through this menu
* send and receive don't unhide the window when opened for the action menu. It does navigate to the right tab. The other actions do work (sign, verify & debug window)

Clicking "Toon" (= macOS native show) does work, suggesting the GUI uses some non-native method of hiding.
{
    Q_OBJECT
public:
    static const std::string DEFAULT_UIPLATFORM;
    explicit BitcoinGUI(interfaces::Node& node, const PlatformStyle *platformStyle, const NetworkStyle *networkStyle, QWidget *parent = 0);
    ~BitcoinGUI();
    /** Set the client model.
        The client model represents the part of the core that communicates with the P2P network, and is wallet-agnostic.
    */
    void setClientModel(ClientModel *clientModel);
#ifdef ENABLE_WALLET
    /** Set the wallet model.
        The wallet model represents a bitcoin wallet, and offers access to the list of transactions, address book and sending
        functionality.
    */
    bool addWallet(WalletModel *walletModel);
    bool removeWallet(WalletModel* walletModel);
    void removeAllWallets();
#endif 
    bool enableWallet = false;
protected:
    void changeEvent(QEvent *e);
    void closeEvent(QCloseEvent *event);
    void showEvent(QShowEvent *event);
    void dragEnterEvent(QDragEnterEvent *event);
    void dropEvent(QDropEvent *event);
    bool eventFilter(QObject *object, QEvent *event);
private:
    interfaces::Node& m_node;