Is this a sorting bug?

[KOE]

Title: Is this a sorting bug?

I select a filter that shows me only a particular category. When I click on the “received” field to sort the list I notice that it does not sort the date properly. Everything from this year “2002” is in the middle of the emails from “2001”. It works fine (sorts in proper chronological order) when I am not applying the category filter. Is this a sorting bug?