Are there instances where modification time is not supposed to change?

[Patrick Doyle]

> For another fun misfeature, I have taken to using the -n option with
> gzip all the time recently. It turns out that gzip has started writing
> a timestamp into the compressed output. This means you can compress two
> files with identical content and get different .gz files :-( Caused a
> lot of trouble for my hard-link tree backup setups.
>
Actually, gzip has done that for the last decade or so.  And, yes,
I've been annoyed by it as well, for the last decade or so.

--wpd