Sticky Threads - Topics Order
 

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They are ordered by the same method that you order the rest of the threads in the forum. So, if by last post date, then they are ordered by last post date. And, the query for all the threads is made in the same query (order by sticky makes sure the stickies are ordered first in the query results). I think you would have to actually modified the code in forumdisplay.php in order to change this - I don't think you could just do it with a plugin.