There has been a slight change in how MIME types for uploaded assets are determined.

Previously, users uploaded a file from a source URL and Contentful would store the MIME type the source server specified for that file, regardless of the actual MIME type of the file. For example, if users processed a PNG file but the source server specified the file’s MIME type as “application/octet-stream”, then this was the information that Contentful stored and served in its own responses as well.

What's changed: Now we auto-detect the file's MIME type and store the correct information. So in the above example, Contentful's response would now server the image with the "image/png" MIME type. Only when the automatic detection can't detect a file type do we use the one the source server provided.