Let me preface by saying I know they're still usable from the equipment menu. Your character won't get nanite fever if you use them. Functionally expired boosts are no different to "fresh" ones. Alright, so a boost is expired. What does that mean, specifically? There's digital fungus growing on them? They're stored on magnetic tape with no ECC and are prey to cosmic ray entropy? Or do the bits just go bad over time, can't hold a full 1 and max out at more like 0.83f ? One could think they're there to remind a player that he/she has boosts available, in case they get missed. A blood-red label with the capitalized text EXPIRED conveys that intention with the clarity of an obituary written on a MS Word birthday invitation template in Comic Sans. So my question is - is this a bug, the work of a renegade UI designer who secretly enjoys confusing people, or is this a premeditated, perfidious attempt at misleading customers into buying new boosts when their old ones are still perfectly valid?
