problem uploading jpgs with exif metadata to Amazon S3 bucket

I have a few Runway sites using Amazon S3 / Cloudfront CDN to host images, which clients have been having problems uploading some jpgs to. For ages, I assumed the problems were memory related, i.e. clients trying to upload huge 300dpi jpgs, but on further testing I've discovered that these files upload fine if the exif metadata is removed.

These files do actually upload to the CDN but Perch seems unable to create the thumbnail preview and when you reload the asset page the link to the uploaded file disappears, i.e. there's an entry for the asset title but the association to the uploaded file is lost, so it can't be added to a content region.

I have no problem uploading the same files on another Runway installation (same version) that uses the default self hosted resources folder, i.e. on the same server as the site.

Has anyone else experienced similar problems or found any solutions?