Different loader.sin in stock ftf and my (also stock) ftf made from PCC

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http://forum.xda-developers.com – I am thinking about rooting my Xperia P, but firstly I made a backup ftf from PCC using flashtool (I have non branded stock ROM 1.54). Then I downloaded stock ROM 1.54 from http://forum.xda-developers.com/show....php?t=2020778, unpack both ROMs and use WinMerge to compare them. I expected that all sin files are the same. And they were, except loader.sin. And now my questios is: why loader.sin is different? My XP has locked bootloader. I downloaded also kernel 1.54 from http://forum.xda-developers.com/show....php?t=1900172 and compared with my ftf with the same result - loader.sin is differen (HowTos)