I would expect that this is implementation specific. You are right that the close button included on a resize should not also be included after calling expand(), so in that way the resize is cancelled.
As an ad creator, I wouldn't think about it. I would do something like start with a banner that is 320x50, then to grab your attention, resize to 320x100 for 7 seconds. If you don't tap, I'll revert back to the default banner, but if you do tap, I'll expand to full screen for the full rich media experience.
In other words, I think that the ad unit is going from 320x50 >> 320x100 >> 320x416 (not 320x50 >> 320x100 >> forced 320x50 >> 320x416).
Does that help?