Why does Facebook behave like a bitch?

Two weeks ago I've changed my social media avatars as a personal condolence message for victims of paris. Today I wanted to update my profile images on Facebook and Google+ again.  It turned out, that Facebook rather than Google+ is such a bitch in terms of post-image-upload-rendering. Facebook's image-uploader renders my image in such a bad way, so that rendering artefacts and smearing occur in it. If I upload the same image to my Google+ profile, none of these errors occur there. 

It's a PNG-file, created with Adobe Illustrator. I've tried different export-settings (JPG, PNG, twp-color/sRGB translation, compression turned off ... ), but it had no effect.