The quickest fix for the data corruption problem is to delete the line
    newfile.seek(file.tell(), 0)
from the rollover() method.

This doesn't fix the inconsistency of tell() and seek(), but it's very low risk.  It's technically a change to the API, that rollover() no longer preserves the seek position, but unless the user was writing only characters from the ISO-8859-1 character set, it wasn't working properly before anyway.