The info "EXIF integrated thumbnail" sometimes gets lost.
Example , here is a screen copy where XnView-classic is in background and XnView-MP 0.84 in foreground, both in explorer mode, **on_the_same_folder**.
Well, the image is pretty large, maybe it is not complete seen in the forum; you can get it separately at this address : http://sebmortum.free.fr/images_publiqu ... lassic.png

You can see the same files in both explorers, they have indicators of integrated thumnails in "classic" XnView, not in XnView-MP.
This bug does not occur in every folder, and probably not in every sort mode.
A clue to try to solve this bug : it seems (from a few examples I tried) that when all the images of a folder contain an integrated thumbnail , the indicator disappears after the first video file shown in the display :
Here, too, every jpg file has an "integrated thumbnail"indicator if open in XnView-Classic :

The indicator of integrated thumnail disappears after MVI_6650, the first video file displayed.