Paul,
The polarisation voltages for an LNB are only in the area of 12-14V aren't they?.
With this size of voltage (90V), It makes me wonder if the SMPS in the satellite decoder isn't faulty?, no appliance should leak these sorts of voltages!.
Just with regard to stray voltages, I've lost count of the number of times that I've recieved a small zap, through either an ear or the side of my face when contacting a TV aerial with a masthead amp on it.
Some of the amps here use up to 22VAC and a shock like this can be quite disheartening, I once nearly fell off the roof of a 3 storey house, because of this. [Linked Image]