when I search for mail the results in iOS7 aren't in chronological order anymore. Both on my iphone 5 and my iPad 2.
I find that any messages that are flagged go to the top before Mail starts sorting in chronological order. I assume that's a "feature" and not a "bug." Is that what's happening for you?
Far worse than that. See this thread, among many: https://discussions.apple.com/thread/5323188?tstart=0
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