Well, if you're using a custom style, they could have something set up to do based on a certain pixel size, then your outer table will increase to that size for a min...
Or you could have a browser cache problem (this happens to me a lot in Firefox, which is why I like Opera more). Force a re-download of the page.
Internet Explorer:
Hold CTRL and press Refresh
Firefox:
Hold SHIFT and press Refresh
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