This is normal, if not logical.

I think it is not (any more) meant to be a "miles to Platinum meter" but just an indication of how your level miles are progressing. On the other hand it used to say "miles to Platinum" (mine does not show this text any more). I think that originally it was set indicate progress until the next tier until someone realized that it is easily possible to have many more than 70.000 level miles and adapted it, but not with any particular logic.