Depending on the type of tile floor you have this may not be unusual. We have what I'd describe as a sculpted tile (with high bits and low bits) and I just pick a specific tile and use it. Doesn't matter in the end if it's high or low, it still changes. I could drag it into the laundry room, where we have a very flat linoleum but there's no free space there to store it. Without thinking one day I plopped it down on a hard rubber map one day and lost about 20 pounds.

Although I just checked and I get less that half a pound's difference moving it about.
Oh, and mine is a Tanita as well.