Order of stuff in containers

[SekoETC]

What defines the order in which the contents of a container are listed? Apparently it's a fixed order, since I tried everything to put an item "behind" other items but no matter what I did, it showed up in the beginning of the list. It doesn't matter if it's put in first or last, the order is fixed and I can't figure out the logic behind it.

[*Wiro]

Possibly the item id. The current order is temporary awaiting a solution for books (look in accepted suggestions for the thread).

[SekoETC]

But if it was item id then it would either be old come first, or new come first, and I have another character whose container seems to support the old come first system, but when I tried to put older items in the container on this problem character, the newest item still appeared first.