Certain Imagefield Crop Files deleted after node save

For a simple site I want to use Imagefield Crop in conjunction with FileField Paths and Pathauto to clean up file names of uploaded images.

To do so, I enabled "Transliterate prior to creating alias" and "Reduce strings to letters and numbers from ASCII-96" (using the supplied example file) in Pathauto. Then I checked "Cleanup using Pathauto." and "Convert to lower case." for both the "File path cleanup settings" and the "File name cleanup settings" of the file field (widget: Image with cropping, single image, not required).

This seemed to work at first. But then I encountered the problem that certain image files that I uploaded got deleted immediately after saving the node. And there seems to be a system, depending on the file name: The files "93620015.JPG" and "ÄBC.jpg" (notice the Umlaut "Ä") got uploaded and cleaned up correctly, but the files "PICT1125.jpg" and "ABC.jpg" got deleted at node save.

It seems to me, that file names that are literally the same before and after clean up--but not transliterally--are deleted. I am running MAMP on Mac OSX, which does not differ between lowercase and uppercase with standard "Mac OS Extended (Journaled)" file system. So maybe this leads to overwriting / deleting the cleaned up files created by FileField Paths, instead of the uploaded original.