Memory leak in navigation window

Hi, the main skeleton of my app is a global navigationWindow. This module has methods like 'create', 'open' nand 'close'. Here the close snippet:

exports.close = function(win) {
        console.log('===\nWINDOW before closing:     ' + Ti.Platform.availableMemory);
        navigationWindow.closeWindow(win);
        win = null;
    console.log('===\nWINDOW after nulling:     ' + Ti.Platform.availableMemory);
};

On console I can observe that the memory keeps constant (it makes little noise). But after opening/closing of window ca. 7 times the app crashes.

With xcode instruments of iOS I can observe the memory allocation. And this graphic grows and grows … After closing of a window it sinks a little but then it grows again.

The window is setting to null by code. I think some stuff works against the GC and the memory will not freed.

Any ideas, how can I solve it, where are typical traps?

Best regards

Konrad