Inventory auto sort and stack?

[kram]

How are they getting un-stacked in the first place? I've never seen a case where items didn't stack automatically when you get them or transfer them.

If for example I put "item A" in my retainer. Then tomorrow I'll put again the "item A" and forgot to stack it, that is the time it won't stack automatically. So I have 2 slots inventory for "Item A".