Sounds like a bug. Maybe it's running the "left old zone" event after the "entered new zone" one because blockland.
That sounds like the source of a similar and potentially much more jarring bug:
walking from one zone to an adjacent zone will briefly load the new zone's environment before going back to the global environment
so you're in a deep dark dungeon or whatever and oooh it's like
lava room time
get a touch of reddish ambient light in--
*OUTDOOR SHADOW COLOR*
This could all be avoided,
I think, by using persistent zones which don't revert to global, but it would be good to not have to rely on that