I don't think that's a bug,because the whole MED is a bug it self.
A7 is really great Engine,but OH god,MED is reall pain,it's designed for begginers,that's why they improved FBX and other IMPORT EXPORT tools,so you can use more professional tools such as 3DsMAX or MAYA or even BLENDER,and here comes the problems,so don't bet on it,I am using 3dsmax and allways get problems
importing FBX models with bones in MED,I have tryed so many technics to solve this problem,and finaly I found a good 3dsmax *.X exporter called "PANDA *.X exporter",it's great tool and totaly free,i don't know about BLENDER,but now i can export models with bones from MAX in *.X,and import it in med with no troubles,well atleast for now.
Good luck.