Why does Adobe Premiere Pro modify original footage/asset files (e.g. mov)? (CS6) Background:


A colleague had given me a large 33Gb .mov for use in a project, I
put this file on a backup drive.
I made an identical copy of this 33Gb .mov file and placed it in a folder that I'd use to work on a Premiere Pro Project. 
I ran Adobe Premiere Pro CS6 and dragged in the 33Gb .mov file into the Sequence (imported it) 
Premiere Pro CS6 started conforming the file.
After it had finished, I noticed that
it's Modified Date was just now i.e different to the Modified Date
on the original copy of the file on the backup drive (see step 1)
I ran a BeyondCompare check between the .mov file on the backup drive
(see step 1) and the one that the Premiere Pro project was using
(step 2, 3) and Beyond Compare reported they were different.


I had initially thought it was unrelated file corruption of some kind, but I have checked this several times and got the same outcome, so it's definitely Premiere Pro deliberately modifying the file.

So I am puzzled: these are supposed to be the same file.

Why would there be a need for Adobe Premiere Pro to modify the footage?
What does it do to the file?
Would it not be better to create a separate file if necessary?

I can accept this if that's how it works and it's good to know that it was Premiere Pro deliberately modifying the files and not corruption (so my hardware ought to be healthy). But it makes more sense to me if Premiere Pro made separate modified copies for its own use. Modifying the file as it does hinders my process for checking the integrity of backups; if the original asset footage files were the same as earlier copies then it would be easy to know that the backups are OK.

Thoughts?
It's all about this setting, "Write XMP ID To Files On Import" - which confirms that Adobe Premiere Pro is deliberately modifying the .mov file: http://helpx.adobe.com/premiere-pro/using/preferences.html#WSE3BD4A43-7022-4fe6-97F5-95313935347B

These posts give some background as to why having this setting enabled would be beneficial: one benefit being to be able to skip conforming files by matching the conformed file with the original using the embedded XMP tag :-


http://helpx.adobe.com/premiere-pro/using/preferences.html#WSE3BD4A43-7022-4fe6-97F5-95313935347B
http://www.dvinfo.net/forum/adobe-creative-suite/498627-why-premiere-modifying-video-files.html
https://forums.creativecow.net/thread/205/876064


(Found using Google search term "adobe premiere pro date modified")

(will accept this answer, when 2 days has elapsed)