WinDbg: OutputDebugString() replaces memory on "DBWIN_BUFFER" text!?!

I run into strange problem.
When I’m calling OutputDebugString() it sometimes replace part of my
memory on L"DBWIN_BUFFER" text!?!

Over more, because I’m debugging application layer solution, I may start
it in the test mode under VS2005. And it works fine!
The problem appears only under WinDbg.

The scanning of Internet does not add me hints.
What is happened?
It is not my first experience with OutputDebugString() and I have not
any problems with it before…

Thanks for help,
Michael.