Weirdness is afoot when you light a Jack the Pumpkin. First, mine disappeared in my bags. Search turned it up - it was invisible but I could click the empty-looking square in my bags to drop it. When dropped, it was bigger than normal. lem.to/p/1rib Then it disappeared completely. I came back to my street later and it had reappeared, still large. Teaching it a phrase popped it down to normal size and so far it hasn't vanished again.
This has only been an issue for me with Jack. Lem, Steve, Zille, and Kitty pumpkins seem to be OK.