See for example
<
http://n2.nabble.com/file/n2264328/digesting%2BRSS.jpeg>
— the result of inserting a PNG
— note the .jpeg suffix to the file name.
This happens only rarely.
I have a sense that it's more likely to happen if the PNG is above some size threshold.
Priority: 5 (lowest).
For reference, I attach (as a file, not an image) the PNG file that was interpreted as JPEG:
digesting+RSS.pngEnvironment: Safari 3.2.1 (5525.27.1), Mac OS X 10.5.6, Intel; and I typically drag the image from ~/Desktop to the
Choose File button (AFAIK the ability to drop there is a feature of Mac OS X).
.png extension is present but not shown in Finder: