CREO2 - mass with simplified model

I have a assembly with 2 parts (Mass X1 and  X2). In this ASM i have the relation : Masse=PRO_MP_MASS

When i evalue the "Masse" parameter i find the good value (Masse=X1+X2).

Now if i create a simplified model from this ASM, with only 1 of these parts (f.e. mass X1), activate it and evalue the "Masse" parameter, the result is the same (X1+X2) !

Whereas i calculate the mass property by the frame "Analys" the weight is correct (X1) !

So my question is : Is it possible to extract the mass of a simplified model ?