Unwanted use of file_directory_path() leads to images stored in files/files/images not files/images

Not sure if there is something unusual about my installation, but I find that aggregation item images are being saved into files/files/images rather than files/images.

I can fix the problem by removing the call to file_directory_path() on line 1447, so this

if (file_put_contents(file_directory_path().'/'.$newfile, $data) == 0)

becomes

if (file_put_contents($newfile, $data) == 0)

I think this is logical, as we've already done all the work to generate a valid filename on line 1437's call to _image_filename().