"autoloads" comments in Emacs Lisp files contain the timestamp of the source file to which they refer. This becomes a problem if the source files are patched in the Debian package; the timestamps then are no longer deterministic.
The comments look something like this. The numbers at the end form a timestamp.
;;;### (autoloads nil "sml-mode" "sml-mode.el" (21693 61228 0 0))
They usually come in a file called foo-autoloads.el.
- Emacs seems to support an alternate scheme based on MD5 hashes instead of timestamps.