Sergey,
You are absolutely right. There was no problem with that code and the file wasn't corrupted.
There was a function called close data which was called after all of the data had been written to the file. In the header it said it wrote a summary to the end of the file but it didn't it wrote it to the top overwriting the first line.
It probably used to write to the end of the file but some c*** had changed it and not altered the desription in the header.
Other peoples code. When they bother annotating it they just mislead you.