I can't tell you why it was decided to behave like this. Perhaps it was
felt that, since FileIO is low-level (lower than the file object in
2.x), it shouldn't have to remember and restore the old file position.
That argument wouldn't apply to BufferedWriter, though.

I'm afraid I don't know anything about the padding differences myself.
If you give us more precisions on the subject, we will be able to
include them in the documentation.