trouble with new SD-library

With the new version of the SD-library i have trouble with print to file. The aim is to overwrite the beginning of the data on the file.

I open the file to write on it, with file.seek(0) i jump at the very beginning of the file. With serial.print(file.position()) i receive the confirmation that this has been carried out, but when i print the data it is appended at the end of the file.

Can someone give me a hand?

Thanks a lot!