Solved by jmaronas in post #2 
              
              
                If your loss is L=L1+L2 then the gradients at the input will sum.  Consider: 
L1=f1(x) 
L2=f2(x) 
L=f1(x)+f2(x) 
The derivative w.r.t x will be the derivative through f1 + the derivative through f2. This is because the derivative of a sum is the sum of the derivatives. If your combined loss is: 
L=f…