I got a cooking pot on experimental branch 0.42, and it appears to have 5x1 inventory slot layout. I try to drag single slot items into it, and every item appears red when mousing over a slot. I have tried many different items from food to compass, and none work.
The last experimental branch 0.37 allowed me to put items into the slots (was 3x2 slots) and it only allowed me to put a total of 4 items in, and the slot I put the item into was not the slot it ended up going into.