distributions - derivative of DiracDelta

For the derivative of Dirac-Delta distributions one can show by using partial derivative that $\delta'(-x)=-\delta'(x)$. Thus, I wonder why Mathematica returns

In[1]= Integrate[foo[r] D[DiracDelta[ a - r], r], 
                  {r, -\[Infinity], \[Infinity]}]

Out[1]= ConditionalExpression[-foo'[a], a \[Element] Reals]

The output should be foo'[a] (see e.g. MathWorld). Am I doing something wrong?