With a file whose datestamp is not important to you, first display
that timestamp, then try
gvim --clean -R filename.ext
(with two dashes before clean and one before R; it means "edit the
file readonly with only Vim's own default settinigs as set by the
defaults.vim script")
then when gvim has opened the file
:q
(i.e. "quit"), followed by Enter, to close it. Has the timestamp
changed? If it hasn't, then one or more of your customizations (vimrc,
plugins, whatever) is doing something with your file's timestamp. If
it has, then it might be Windows, but I'm not sure.
Oh, and BTW which version of gvim are you using?
:intro
will give you the short answer to this question, and
:version
will give you the long answer.
Best regards,
Tony.