c++11 thread bug in visual studio 2013?

I recently find that when I tried to use c++11's thread in visual studio 2013, it generate bigger object file and exe file in release mode than debug mode. Is this indicate that the obj file contains more information in release mode that debug mode? That's so weird. Moreover, in debug mode, I tried to debug the program step by step, but the break point and step can not be located as I set in the source file, this behavior is just like in the release mode in which the program does not exactly correspond to the source file due to optimization. So can someone explain this to me? Thank you.