Root cause found: the ladder exit in Mushroom Castle is a touch-type portal, but the engine currently auto-fires only one class of touch portal, so it wants a key press the falling player cannot make. The clean fix touches a portal type shared by the Temple of Time flight ride, so I am doing it carefully rather than risk breaking those flights. Tracked.

Thanks enigmaX, and sorry for the wait. We found the real cause: the way out at the bottom of Outer Castle Wall should trigger anywhere along that bottom floor, but ours only triggers in a narrow spot near its middle, so landing under the beanstalk does nothing. Two other Mushroom Castle maps have the same problem, and all three are being fixed now. Until that's live: if you fall, walk right along the bottom floor toward the middle of the map, and the exit should take you back to Split Road of Destiny.

This is fixed and live now. The exit at the bottom of Outer Castle Wall now catches you anywhere along the bottom floor, just like the original, so dropping off the beanstalk takes you straight back to the Split Road of Destiny. The two other Mushroom Castle exits with the same problem are fixed too. Refresh the game once to get the update, and reply here if you still get stuck.