(late) reply to your answer dating December 17, 2011 Rated 4 out of 5 stars
sorry for my late reply to your answer.
No, the "add date to the file properties" feature does not work properly yet.
As you know, each file (in Windows) has three timestamps: 1) created; 2) modified; 3) accessed.
Whenever you see the detailed list of files in Windows, the timestamp shown is the second one (modified), and you can see the other two by cliccking on "properties". Also in WinZip the timestamp shown is the second one.
If I am not wrong, your add-on sets the third timestamp (accessed) and lets the other two fields empty. So, sometimes Windows adds the current time to such fields. I would suggest you to set the timestamp of the second field (modified) when the feature "add timestamp" is thicked.
I guess that the problem is connected with new versions of Windows, for I am experiencing similar problems with the timestamps of pictures taken with my digital cameras. If I download them on a Windows XP computer the timestamp is ok, if I download them on a Windows 7 or Vista computer, I get the timestamp of the moment in which I downloaded them, but some programs are able to correct the problem (Olympus software is not able, Canon software is).