Image time display discrepancies between product

Question

The following is an example of a problem I've observed in many places in my photo collection.
I have two files taken 8 seconds apart in April 2009 with a Nikon D70 shooting .jpg format.  The files were subsequently imported from the camera memory card using a card reader and Photoshop Elements.  PSE was also used to add tags to these files.
Since then I've acquired Photoshop CS 5 Extended.  The other day I was looking at these files in both PSE and Bridge.  PSE shows the time of these two files to be the same (as it should), however, it adds an hour to the actual time the image was taken to adjust for the difference between the time set in the camera (it was Pacific Time) and the time zone where my computer is now located (Mountain Time).  When I look at the time on the images in Bridge, one of them shows the correct time in Pacific Daylight Time, but the other is showing the corresponding UTC time value, 7 hours later than the local time.  Looking at the file list in Window Explorer shows the "Date" and "Date taken" values to be the same as that shown by Bridge.
There were two other images taken shortly before the first one mentioned above and they show the correct local time.  The two files that followed the UTC timed file also show a UTC time value.  Then following that the next file shows local time and then there are a number of files showing UTC for time.
If I look at the two files with Windows Notepad so that I can see some of the text strings in the exif data portion of the file, the first file has a couple different places where time is shown in the format "...hh:mm:ss-07:00" and the other in the format "...hh:mm:ssZ".  The time value is preceded by the date in yyyy:mm:dd format. It would appear that Bridge is reading these values and displaying them, while PSE is getting some other time value from the file. Here is the actual string from the file that displays in UTC:
     exif:DateTimeOriginal="2009-04-05T17:08:10Z"   exif:DateTimeDigitized="2009-04-05T17:08:10Z"
and for the file that displays time in local time the string is:
     exif:DateTimeOriginal="2009-04-05T10:08:02-07:00"   exif:DateTimeDigitized="2009-04-05T10:08:02-07:00"
I've observed this same discrepany with files taken more recently with a Nikon D700 and images in NEF format.  I think I can reasonably eliminate the possibility that this is a camera caused discrepancy.  I suspect that some program is actually reading the local time and offset, then writing that back to the file as a UTC time value.  The behaviors of PSE and Bridge seem to point to the fact that the two programs are extracting time from different fields / strings in the file.  At this point the occurrance of the problem seems random, at least I've not been able to discern a pattern and reproduce it at will.
Although this is not a catastrophic problem, it does cause confusion.  I've also looked at these files in Lightroom, which on initial inspection appears to get the same time values as Bridge.  The down side of this is that files in Lightroom are sorted into time order, which may not be the order they were taken.  Although I recognize that these products may not have been design for complete compatibility, it sure would be nice if they all treated time in the same way.

Answer 1

I believe I now have more information about how PSE works and therefore need to slightly correct my original post.  It looks like PSE takes what ever time it finds for the photo's "time taken," converts it to UTC, then converts it to the local time on which PSE is running.  That will explain why two images taken seconds apart, with on having time coded as local time plus UTC offset and the other having an absolute UTC time, display the time taken in local time.  On the other hand, Bridge (and Lightroom) just displays what ever time it finds in the file.