thumbnail not matching filmstrip/open file view

I am having a new and curious problem.

storage method: I take the SD card from the G9 and copy it to a western digital 500 GB Passport during trips.

When I get home, I copy the passport files to a 500 GB W.D. Prodrive.

I then do any editing, sharpening, etc from the Prodrive, keeping the passport files untouched.

But for one folder from Roatan 3 weeks ago, the Prodrive Thumbnail picture does not match the 'filmstrip' view and does not match the view if the file is opened.

This non-matching only seems to be effecting the first 20 files. Later files in that folder match correctly.

When I go back to the Passport files, all match correctly.

Any thoughts on how this can happen?

I am guessing the easiest correction is to re-copy and overwrite the Prodrive files from the Passport files.

Wondering if anyone else has had this happen?

Upon further review,

Copying over the Prodrive files made no improvement.

The filmstrip view and opened view match the Passport thumbnail.

The Prodrive filmstrip view and opened view also match the Passport files.

What does not match is the thumbnail view on the Prodrive and over-writing did not change this.

Dave