I have found one more bug in SimpleMP.
I applied these settings (see screenshot) & closed SimpleMP.
Again started SimpleMP & changed the settings (screenshot) & pressed OK.
Now if SimpleMP is minimized then it is neither visible in taskbar nor in system tray.
I have informed the author about it & received a reply mail from him. He told me that he will improve SimpleMP very soon.
Anyway, I liked SimpleMP very much coz of its small size, simple GUI & equalizer feature.