SIPS or Image Events Problem

I use this code to automatically create scaled images and thumbnails for my website:

on open draggedItems
repeat with currentFile in draggedItems
tell application "System Events"
    set home_directory to (path to current user folder) as string
end tell
    set image_path to (home_directory & "Sites:barridoff:2005:images:")
    set thumbnail_path to (home_directory & "Sites:barridoff:2005:thumbnails:")
tell application "Image Events"
    set openedFile to open (currentFile as alias)
    set properties of openedFile to {bit depth:millions of colors, color space:RGB, resolution:{72.0, 72.0}}
    scale openedFile to size 750
    save openedFile as JPEG in image_path with icon
    scale openedFile to size 125
    save openedFile as JPEG in thumbnail_path with icon
    close openedFile
end tell
    on error error_message
    display dialog error_message
    end try
    end repeat
    end open

It works perfectly, except that for some images, a one-pixel wide/high black line appears along one of the edges of the images, usually the top. It appears (though I’m not certain) that this odd black line replaces the top line of my image, which is worse (if it just added the line, I’d figure out a way to automatically crop it out; this way, I’m rather stuck).
I can’t for the life of me figure out what’s causing this or how to fix it.
Any indeas?