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.
#include <qt/guiutil.h>
#include <qt/bitcoinaddressvalidator.h>
#include <qt/bitcoinunits.h>
#include <qt/qvalidatedlineedit.h>
#include <qt/walletmodel.h>
#include <base58.h>
#include <chainparams.h>
#include <primitives/transaction.h>
#include <key_io.h>
#include <interfaces/node.h>
#include <policy/policy.h>
#include <protocol.h>
#include <script/script.h>
#include <script/standard.h>
#include <util.h>
#ifdef WIN32
#ifdef _WIN32_WINNT
#undef _WIN32_WINNT
#endif
#define _WIN32_WINNT 0x0501
#ifdef _WIN32_IE
#undef _WIN32_IE
#endif
#define _WIN32_IE 0x0501
#define WIN32_LEAN_AND_MEAN 1
#ifndef NOMINMAX
#define NOMINMAX
#endif
#include <shellapi.h>