Cannot edit word file in FTP

Dear all,

i have a problem about FTP in Server 2008 R2

after i open word or excel in ftp via internet explorer 8 or 9 it show FTG log on

i insert my username and pass and then i edit file word and save it

but word file don't update follow i edit it show old modified date not last update.

i think FTP protect file for edit, or not