It seems the way the GridModifyPlugin updates the ticket means that certain parts of the notification flow is bypassed. I don't know the Trac source very well, but I tried to trace through the code and came across this:
Line 180 in trac/ticket/notification.py looks like this:
for change in TicketModule(self.env).grouped_changelog_entries(ticket, when=modtime):
The call to grouped_changelog_entries() returnes an empty list when using gridmod, but NOT when using the Trac UI. The result is that the notification flow is not updated correctly. In the ticket_notify_email.txt the $changes_body won't be set correctly, which means that the email notification doesn't show WHAT was changed using gridmod.
Don't know if this is related to the 1.0 release.