Polynomial derivative causes Prime to Crash?

[Spybot]

Hello!

Perhaps just trying to save some time while finding the derivative of this polynomial function:
d/dx(5x^(3/5)+4x^(3/4)) ... using the Prime Virtual Calculator, it failed causing the Emulator to crash, then I tried to solve it separating each term to find out the symbolic results are no the ones I expected.
   
   
I noticed that evaluating the derivative numerically it returns correct values... but symbolically I'm not sure, what do you think?

Thank you.