Sed --in-place creates new file

Hi,

Using sed for windows version 4..2.1 (url :
http://gnuwin32.sourceforge.net/packages/sed.htm)

sed -i "s/to/ti/" test.txt will modify test.txt (ok) but will create a
new file "sedGnChQb"
sed -i"" "s/to/ti/" test.txt  does the same new file

How to avoid sed to create a new file ?

Thanks a lot.