weird results for the solution of a simple equation !!!!

[arvin84@…]

OM ver.: 539229e

for the simple following model:

model a

Real x1;
Real x2;

equation

x1 + x2 = 0;
x1 - x2 = 1;

end a;

i get the following wrong answer:

x1=0.5;
x2=0;