Note to self: this happens in Safari when "accept" attribute of the file input element includes any natively supported image format like "image/jpg" before custom extensions like ".cr2". Additionally, when custom extension ".tiff" comes before a RAW format, Safari internally converts the preview JPG embedded into the RAW file to TIFF, then loads that. (???) I have no clue why anybody at Apple thinks its a good idea to break standards like that in such a horrible and completely unpredictable way. The fix is easy enough though: Just remove the accept attribute from the file input. Unfortunately this leads to no pre-filtering of accepted file formats in the OS file browser. Still better than no RAW support in Safari.