[bubblewand]

1) Not for "self-funded"—many plans are managed by big insurance companies, but funded by employers. No restrictions there.

2) Not for plans that are (IIRC) two years old or newer. I'd be shocked if there aren't a bunch of shenanigans going on with this loophole.

[mindslight]

also 3) many "insurance" companies are in the provider game, meaning they can preferentially shuffle surplus to their other arm

(2) and (3) were part of what I meant by a lack of regulatory bandwidth in another comment. There are rules that could be enforced to promptly impose steep penalties for a company that tries to skirt them. But they just aren't, so after one company starts doing it the rest inevitably follow suit.