Segfault in QTextStream

There seems to be a bug in QTextStrem/IO device class when used with threads. The attached example reproduces the bug. The effect is more visible on slower machines or if more than one instance of the application running (the segfault is random).

Note:
The way the example is written is a bit unusual, as it just continue to write to the same stream (the QTextStream is a member of the class), also seek is never called to go back to the start of the stream. But it still should not segfault as it does.