Is it normal for an address to drop off the historic shares listing in the pool?  The reason I'm asking is that every time I checked my balance by typing in a few letters of my address, another address with the same sequence of letters would always appear.  This other address had a very large amount of ARO in it and its hash rate was really high.  As of a couple of days ago, this address no longer shows up when I look up mine.  This was tracked to the following address on the Arionum block explorer: 2MsskkbgsmMtjpA7qjjSfqwfvZkZzKHNvRSL2JWYT8Pid8ZZt6GpnfLjiwYc52Df6uwEp1QugWARKKp qWDJwWL38

Edit: Is it normal for the Historic Shared to decrease in size from time to time?  I've seen these drop by as much as a few million at times.