Republican leaders are pleased their health reform plan would lower premiums on average up to 10%, according to the Congressional Budget Office, and shave $68 billion from the deficit. But there’s an odd feature to the reform plan.

It makes coverage more expensive for older or sick people.

It does that because if you raise their rates, fewer of them will get insurance, lowering costs for people who do have insurance. And that lets insurers lower costs more for the young and healthy, who need fewer services, which is why costs come down in the GOP plan.

“Some provisions of the legislation would tend to decrease the premiums paid by all insurance enrollees, while other provisions would tend to increase the premiums paid by less healthy enrollees,” the CBO analysis says.

“Improved average health status of insured people would lower average premiums; at the same time, the pool of people without health insurance would end up being less healthy, on average, than under current law,” the CBO says.

So the GOP plan would add about 3 million people to the insurance rolls by 2019, while sicker and older people lose insurance, and the overall percentage of uninsured stays the same.