image/pjpeg mime type?

This isn't so much a bug as a query, and given that we're using an older version of Jira it may be moot.

What I'm wondering is why the mime-type for screenshots created using the Java applet is image/pjpeg?
I believe that this is an Internet Explorer-specific mime-type, but shouldn't it technically be image/jpeg or image/x-pjpeg?

It's all rather semantic really.. but just curious.