Autoshifting travel form was never mentioned as a bug. Not all the forms work that way. There is a “mount form” as mentioned already in this thread that does not work the way you claim. This does not shift into other form automatically.
The point is that, while in “mount form”, it is an oversight that there is an auto-shifting feature in water that kicks off the passenger. The form does not otherwise auto-shift.
Changing this does not affect the gameplay you mention you like, in any way.