Ah, it might be a bug report instead of a feature request, then. I'd drawn about 2 dozen tiles, swapping between world/sprite/item/player a few times and placing them in the room. I switched back to the "Game" tab and when I returned to "Room," everything had reset to the default pick-up-floppy-disks mode. It's likely that I did something else in the interim, but I admit I wasn't paying close attention at that point. I almost certainly switched between tabs, because I had the Pulp documentation up at the same time.
As Neven said, having a keyboard shortcut to save will get you in the habit to save often, but I was still getting used to the UI. (And although it did wipe out everything, it's definitely not a big deal as I was just experimenting to see how much I could do with it. I can't devote more time to this until I've finished my main game).
You completely overestimate my patience 
Seriously, though, a lot can be done with swapping tiles, and having an explicit demonstration like your code would be great for example projects and/or the documentation. After seeing more of the Bitsy projects, I've got a better feel for how these games are usually structured and how they manage text displays.