To fix your issue would probably require a new switch for /hadd and /hload to append new items instead of inserting them. I see the -a switch is available.
The reason that mIRC inserts at the beginning of the linked-list is because it is an easy, low cost thing to do. To insert entries at the end of the list you would either need to iterate all the way to the end of the list which would kill performance, or double the number of bytes for each slot in order to hold the pointer to the end of the list (which on today's modern PCs may not be that much of an issue).
