Is this an AE bug?

HI lately I`ve been working in a script that makes use of the onActivate() method on a window ( type palette)  but I`ve been facing a problem It seems to be that AE is calling the method even after the window is closed. Maybe it is only on my machine. Test this code

var win =  new Window ("palette");

win.onActivate = function(){app.project.createComp()};

//just to fill the window

win.add("button",undefined,"Is it a Bug? Please help");

win.show()

The triky thing is once you close the window try jumping between AE and any other window that you have open  you will see that AE keeps adding comps every time AE  becomes the active window. What´s going on?

This seems not to be the case when you use window of type dialog But I do need it to be of type palette.