Thats a known bug with my 4.2.x versions. 

It has to do with how .NET sorts the list of files.  Basically the code sorts the list of images to determine what items to display on each page, then when it goes to display the actual page it re-sorts the list.  The MS sort routines are an "unstable sort" which means that the second time the sort is done, identical value may (will) come back in a different order.  So what happens is the first part of the page adds the images, but the second part of the page finds a different list of images to actually draw.

Some solutions you might want to try is sorting by filename, or adding some text to whatever you are sorting on so that everything has text.. eg.  if you are sorting on title make sure that every image has a title (and that no 2 are the same).  The actual fix in the code is rather complicated as I needed to rewrite a bunch of code to get rid of the double sorting of the list.