Some more info,
When I do `C-h v auto-revert-use-notify` in that file buffer in emacs 24.4, I get
auto-revert-use-notify is a variable defined in `autorevert.el'.
Its value is nil
Original value was t
Local in buffer abcd.txt; global value is t
But in emacs 24.5, the same `C-h v` shows
auto-revert-use-notify is a variable defined in `autorevert.el'.
Its value is t
It's unclear to me what's changing the local value of `auto-revert-use-notify` to `nil` in an emacs -Q session on emacs 24.4. And as the effective value of that var in that buffer is nil, auto reverting works in emacs 24.4 right away without having to manually change the value of that var to nil.