Mass less

So, the official metal lump that signifies the mass of one kilogram appears to be shedding mass: it is 50 micrograms lighter than the average of several copies. Either it has gotten lighter, or the copies have, on average, gotten heavier. What could cause this? My first thought is radioactivity, but I would assume the physicists in charge would think of this too (the article doesn't say). But then, discussing it with Logan, we came up with better ideas: 1) A ghost inhabited the sample, and has now left. It is well known that ghosts have a mass of 0.00005 kilos. 2) Greys. Not sure how they did it, but aliens are crafty. 3) NASA faked the kilogram. 4) Hoagland is in charge of the mass, and the hyperdimensional physics dictated the -- oh, screw it. You know the deal: pretend this is a pareidolia post, and make up your own reason. Best one wins nothing. Good day sir!