Why won't stacks stack with other identical stacks from another Luanti session?

[SwissalpS]

Example:
1 Fill up several chests with identical settings and identical contents.
2 Wrench the all --> they stack nicely.
3 Put that stack into some other chest.
4 Restart the server.
5 Fill up some more chests just like in step 1
6 repeat step 2
7 when you repeat step 3, the new stack doesn't stack with the old stack. Instead they use up another slot.

[OgelGames]

core.serialize is not deterministic, and neither is this:

wrench/functions.lua

Line 174 in 02928b9

for name, meta_type in pairs(def.metas or {}) do

It might be possible to implement our own deterministic serialization function, but I don't know if it's worth adding that extra complexity just to make things stack.