It is set to file's last modified date on purpose.
It works this way : If you are visiting for the first time,
you browser does not send any date headers.
OpenGrok sends the file's last modified date for almost all requests.
Next time you visit the site, a good browser (and robots) send
a "If-modified-since" header, if the file hasn't been modified since
then,
opengrok just sends "not-modified" header and closes the connection.
(it is less burden on the server)
for a given file-modified date, for all possible requests,
the responses are the same. If the file date changes, then it is
possible that
some responses will change. It is much faster to just do a fstat
rather than access CVS history and parse the date.
Instead of being slow + 100% accurate, I am being fast + 95% accurate
That is make the common case faster principle.
Giving 1.34'th date for 1.2 vs 1.3 is not accurate, but it fast and
works,
and is invisible to casual users.