Dear all, I found out that when differentiating a power it is tested whether the exponent is real. If this is the case, code is executed that assumes that this exponent is a numeric. Hower, because we also have real symbols nowadays this is not correct. Besides, why would differentiating x^I need a special case? Its derivative is simply I*x^(I-1). Therefore, I changed this test into a check whether the exponent is a numeric. I will also backport this change to 1.3. Best, Chris