Something very strange......

[FlFishOn]

There's really nothing I know of that would prevent a site from doing what you describe. I'd imagine it's a +EV play from the site's prospective. Makes sense to me. Take a few
good starters away from the regulars, dish 'em out to the new players, movers-up. Every one will be happy, well, not quite.

To test for this is nightmareishly complex. Any site doing it would be beyond detection.