When I am running my project in debug mode in Visual studio, some leaked objects of class StringArray were left in the memory.
This is not happend when I am running in release mode either into Visual studio environment, or inside the command prompt window.
But, a question is remaining to me, just for the completeness of this issue: Why the leak detector handles the class and its objects (StringArrays) separately?
The leak detection is a juce feature, not something that the OS or compiler adds - it can only work on classes where you explicitly add the JUCE_LEAK_DETECTOR macro.