On my computer too, I can reproduce the behavior you described ("a window appears above the taskbar on the left side")
According to msdn, if you use $WS_EX_NOACTIVATE and want your window to appear on the TaskBar, then you need to add the ExStyle $WS_EX_APPWINDOW
BitOr($WS_EX_NOACTIVATE, $WS_EX_APPWINDOW)
I tested it and it works. When the GUI is restored from the TaskBar and another window partially covers it, then clicking on your GUI doesn't bring it to the foreground (which is the purpose of $WS_EX_NOACTIVATE)
Hope it helps