Problems with camera RAW and loading files into photoshop layers, PS script load files into stack

Hi. A frustrating morning trying to load 15 files into a stack for blending. Both Camera Raw load images into PS layers and PS scripts load files into stack stopped after loading two of the fifteen selected files. Something to do with file names - the name structure was in the form _0071234.nef. Moving the files into a new folder and renumbering them sequentially using a three digit sequence solves the problem, though why this is now needed is not clear. Hope this helps if anyone else has the same bug.