Sorry Charlie (sorry), but it is a very well-known and unofficially documented issue with IE. It does not respect content-type (authoritatively).
PS> If it were me I'd let IE go on with it's buggy behavior, i.e. sans kludge -- H4sICNoBwDoAA3NpZwA9jbsNwDAIRHumuC4NklvXTOD0KSJEnwU8fHz4Q8M9i3sGzkS7BBrm OkCTwsycb4S3DloZuMIYeXpLFqw5LaMhXC2ymhreVXNWMw9YGuAYdfmAbwomoPSyFJuFn2x8 Opr8bBBidccAAAA= -- MOTD on Boomtime, the 57th of Chaos, in the YOLD 3168: Everybody was a baby once, Arthur. Oh sure, maybe not today, or...or even yesterday, but once babies chum. Tiny, dimpled, fleshy little mirrors of our us-ness, that we parents hurl into the future like leathery footballs! And you got to get a good spiral on that baby, or evil will make an interception! Ready...break! One, three, thirteen, twenty-six...HIKE! Go deep Arthur! Go deeper!!
