Neal - I was able to reproduce this on 2 different EAS accounts using my iPhone. It's been reported to the developers.
As an aside, I created a multi-day event that was also an all day event. It shows on my iPhone, it shows on the calendar of the person I invited, but it doesn't show in my SmarterMail calendar. Not sure if you created one event for WWDC or individual events for the days you'll be at WWDC, but I'm not sure that would necessarily matter.