Photo Gallery – Date Taken

I have numerous .MOV files (recorded with iPad or iPhone).    These are typically stored on a NAS, and the folders are included in Photo Gallery.  

Photo Gallery displays information about each file in a panel on the right hand side of the screen.   At the top there are People Tags, then Geotag, Caption and Descriptive Tags.    Further down, there is a heading "Information" under which is various data including "Date Taken".

In general, I assume the Date Taken field comes straight from the embedded date/time info in the file.     And I can examine the file with the MediaInfo tool to confirm this is correct.

Curiously, if I copy a .MOV file to another folder (also part of the Gallery), Photo Gallery (for the copied file) displays a different value for Date Taken  - it Displays the Date/Time that Windows Explorer shows as the Date modified.    The particular date/time displayed is not meaningful to me (it is some months after the actual Date Taken, and many weeks before today).    Note that windows shows the same "date modified" value for both the original and the copied file.

So, why does Photo Gallery display the wrong value for Data Taken for a file copied to another location?    Can this be corrected - ie force Photo Gallery to look inside the file to get the correct value?