FLL5359-4F e FLL5359-25F Stabilization problem

I'have checked that the following Eudyna devices: FLL5359-4F e FLL5359-25F are instable beyond their operating frequencies, i'have tested them on Microwave Office.
Trying to use techniques for avoiding instability (resistor to ground, ecc..) there is little improvement


Have someone experiences about these kind of transistors?

Thanks