Sort by 'post' does not work in the list of reputation changes. When you press 'post' it is sorting it by 'time' instead.
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The sort by post or by time is working daily only meaning sorting the list of daily events either by post or by time.
See the profile of anyone with more than one event in some days to see it working.
The reputation history is always divided into each day that reputation is gained, there's no getting around that. The difference between sorting by "time" and "post" is: