It seems to me, I found the reason of such behaviour.

The thumb preview for newly added image was generated incorrectly (the colors just mashed, unfortunately I cannot attach the snap shot to show it to you).

Therefore I couldn't find the image, though it was actually present in the gallery.

The source image is as follows: http://www.educopark.com/Users/Uploads/2d411e4e-6096-43f2-bfbb-9a88e1cb550d/ship-change-direction.jpg

 

And if I upload the same image on your demo page (http://www.cutesoft.net/example/general.aspx), I get the same wrong thumb image!

 

Any ideas why the thumb image preview is not properly generated?

 

Sincerely,

Andrii Kovalchuk