Hidden trackable information in games sucks!
I play games for fun and pursuing the goal to win the game is fun! :)
Now the question: With the home land of the shapeshifters regarding the transformation cost of the dragonmasters, the actual home land of the shapeshifters is meant, right?
Not sure what you mean by "actual" Home terrain of the Shapeshifters. (I suppose you may have had in mind the German "aktuell", that is "current" in English, "actual" is something like "tatsächlich" or "eigentlich".)
In any case, there is only one Home terrain that the Shapeshifters can have at any point in time and the game has no memory of any previous Home terrains they may have had before. The Shapeshifter's Stronghold ability lets them change it, but when they do change it, they change it for all intents and purposes, including what the Dragonlords have to pay to transform it.
These are the current official rules, the upcoming changes to the Shapeshifters might modify something about it.