Dynamic linked files not getting overwritten during patch Installation

Hi,

I have many .xml dynamic linked files in a single component . After Installing Update.exe created using Patch design only few files got updated and some did not get updated. The files which got updated date-time stamp shown by them after installation is the date when those files were added to patch (checked in to TFS) where as one of the file which was checked in to TFS on same date-time stamp shows the date-time stamp same as the patch installation date on user machine.
Although all files were checked in at same time and are dynamically added in ism under same component then why on Patch Install they show different time stamp. (Updated file shows date when it was added to patch whereas file which didnt got updated shows date when patch was installed on user machine.)

Thanks