I think this is really weird and despite having done some searching I wasn't able to find any info related to this problem.
I'm setting up a backup server with a Raspberry Pi running raspbian who will communicate to a Windows 7 PC. What I did was program auto mounting for an external drive attached to the Pi, after doing a manual backup of the files from the W7 PC. Then I shared said mounting folder over Samba and everything works great.
The thing is that I want to use a program called Synkron over windows which can monitor 2 or more folders, detec any changes and copy over the new/modified files periodically. However, when I press "analyze", the programs lists all my files (in the ext drive) as obsolete, and I've discovered that the problem is that Samba (or the Pi itself) is changing the last modified date of the files, substracting exactly 3 hours to each of them. When I remove the drive from the Pi and re analyze it connected to my PC all the files are back to normal and they show up as ok.
This exact situation has happened with 2 different sets of Raspberrys, raspbian installations, external drives, windows PC and files. Also, I checked the date on both Pi's and it was correct every time.
What do? :/