I posted a not so rigth answer, here the truth
Yeah. You die. What is stupid. But there is absolutely no necessity for this. The thing is the following: To make the transformation visible, one of the char's changeable attributes (HP, mana, food etc) has to be changed. And the current script takes 10000 hitpoints away, and adds you immediatley after this your old hp. So the reduction kills you. But as I said: that is useless, even one point would be enough; why 10?! I don't understand why someone whould do this. There is no comment whatsoever in the scripts that this has been done on purpouse. So I think it is a bug (human error).
I can tell you that this will be changed with the vbu (the changes are already done).