Wordpress - Uploaded images don't show in Media Library if there are special characters in IPTC Keywords
I have tested this with an image I created myself with Photoshop where I inserted the word "Süss" in every thinkable IPTC field.
I uploaded it to my WordPress 4.6 installation, which has no image handling plugins installed. The uploading went smoothly, the right thumbnails were created in the uploads directory and the caption field was loaded correctly from the corresponding IPTC field.
Also, the thumbnail was displayed correctly in the media library.
So, I am inclined to say that this was indeed a bug that has been solved since.