I'm not really that familiar with Sonic 3D Blast, but trying out the new DX beta, I find it weird the way Tails and Knuckles continue to take your rings even after you've visited their special stages. Maybe they're storing your rings so you can't lose them or something? Or is there some additional reward if you give them enough? I just find it really confusing. It also might be nice if they only took the amount they needed to open the bonus level, rather than all of them.
Of course, if there's a reason they behave the way they do, feel free to ignore this.