I've seen mine interpret walking as elliptical before, usually if I've been wearing a rucksack and have my watch hand holding the strap as I walk - the upwards orientation of my arm seems to be the reason. I don't quite follow the "only picks up walking as an IQ event" - it doesn't automatically start activity recordings, it will only give you a GPS track and so on if you explicitly start an activity. If that's what you're asking, an IQ event is exactly what you should expect.
