stoichiometric coefficient in reaction panel
 

I am using reaction panel to have my reaction model. My reaction is:

aA + bB --> cC +dD

I found that the result is different if I fill the stoichiometric coefficient as

A + (b/a)B --> (c/a)C + (d/a)D

Why is it so? Actually is there any rules of thumb in filling stoichiometric coefficient in reaction panel?

Please help. It is urgent.