As the title suggests, I attempted to "Split" a Baby Bear pumpkin which I'd placed in a Wooden Box. Once I selected the option, the pumpkin disappeared and I received nothing in my inventory.
I did see a thread which someone posted stating they ran into the same problem with a head of Colewart they'd stored in a Wooden Box, but it seems Jorb's answer for that was related to the "Plenty" stat which is applied to things produced from a field. This Baby Bear, however, came out of a Planter's Pot so I don't know if it would be affected by any "Plenty" modifier since every one I've split thusfar as always produced 2 Flesh and 12 Seeds.
If this is old news, I apologize for wasting forum space.