When I request a cachelist, this is sorted on de date; however in some circumstances this leads to problems in the sorting: when you request the list a second time the order of the caches is different.
As long as all the caches with the same date stay on one page it is not really a problem, however if they are split on pagebounderies you will get part of the caches from the first page also on the second page; missing caches that should be on the second page, but are now on the first page.
See for example the list of new caches in the Netherlands where 29 caches are added on the 19th of july: http://www.geocaching.com/seek/nearest.asp...&submit3=GO
Go there and refresh the page a few times, you will see the caches change place.
This also seems to happen on other cachelists based on dates, like found-by-cacher and placed-by-cacher
Simple solution would be to also sort it on GC-code or on the guid.