For both the correctly displaying and incorrectly displaying thumbnails, the setting for
Image data-->Treat image as is set to Default.
So if you open the above URL and scroll, the first Thumbnails all look to be formatted as expected. But if you scroll way down (sorry, lots of images on this page), you'll begin to see the problem thumbnails.
If you search for the term 'Androscoggin', it should bring you to an area where the zoomed thumbnail formatting is evident. There should be a Nuthatch and Warbler beside and below that don't look to be formatted correctly (all three are set to Default on the image data setting).
Any guidance would be greatly appreciated. Not sure if I have a setting wrong and this is the expected behavior or is this a issue?
As I see the thumbnails are smaller than the required size, therefor the skin thinks they are "tiny", so employ a different type of fitting. I will check why this happens. Perhaps using more columns would never end up in this scenario. Also, it seems you are using all thumbnails as preloaded, therefore all of the images get loaded on page load. This odd behavior, however, never happens with post-loaded thumbnails. I suggest using the default value: 20.