I reported this already years ago, don't know why this was never fixed.

The math node won't raise negative numbers at all, not even by integers, but will return 0.0f in all cases. I stumbled across this again after wanting to raise a gradient image by 2 and just got the positive gradients raised by 2 and the negative ones set to 0. Imho the math node needs because of performance and usability a reimplementation anyway (looking at a trace, this is just mad). But for now I guess this should be fixed straight away, so that the bug doesn't creep into any future implementations.

I attached a patch to solve the problem.