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

• 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.