There was even a theory that he had taken bad medication. However, the idea that he orignally supported the ACA mandate's repeal is now confirmed:
"CBS News’ Jan Crawford confirms widespread rumors that Chief Justice John Roberts initially voted to strike down the Affordable Care Act’s individual mandate, but decided midway through the opinion drafting process that he could not support this constitutionally unjustifiable result. In what may be the biggest revelation of her piece, Crawford also reports that pseudo-moderate Justice Anthony Kennedy led the internal lobbying effort to bring Roberts back into the right-wing fold:
Roberts then withstood a month-long, desperate campaign to bring him back to his original position, the sources said. Ironically, Justice Anthony Kennedy – believed by many conservatives to be the justice most likely to defect and vote for the law – led the effort to try to bring Roberts back to the fold.http://thinkprogress.org/justice/2012/07/01/509359/supreme-court-springs-a-leak-leaks-to-conservative-pundits-may-have-started-more-than-a-month-ago/
“He was relentless,” one source said of Kennedy’s efforts. “He was very engaged in this.”
But this time, Roberts held firm. And so the conservatives handed him their own message which, as one justice put it, essentially translated into, “You’re on your own.”
The conservatives refused to join any aspect of his opinion, including sections with which they agreed, such as his analysis imposing limits on Congress’ power under the Commerce Clause, the sources said.
Instead, the four joined forces and crafted a highly unusual, unsigned joint dissent. They deliberately ignored Roberts’ decision, the sources said, as if they were no longer even willing to engage with him in debate.
So the question begs: who are Crawford's "two very reliable sources?" What's clear is that there aren't many possible sources for the well connected conservative reporter:
"Crawford cites two unnamed sources, and there are a very limited universe of people who could have revealed this information to her. Only the justices and their personal staff would have access to this knowledge, and it is highly unlikely that a clerk or secretary would be willing to risk their entire career by revealing the Court’s confidential deliberations to the press. Crawford, moreover, is a very well connected conservative reporter who has, at times, worked closely with the Federalist Society to drive conservative legal narratives. Nothing is certain, but it is likely that one or both of Crawford’s sources is a conservative justice."
So it is that what may have been going on is that the conservative justices were doing their level best to put conservative pressure on Roberts via leaks to favored conservative media, like Geroge Will who had urged Roberts back in May not to be "cowed" by comments of President Obama.
" as Linda Greenhouse points out, it is possible that the Court started springing leaks more than a month before Roberts handed down his opinion:
Around Memorial Day, a number of conservative columnists and bloggers suddenly began accusing the “liberal media” of putting “the squeeze to Justice Roberts,” as George Will expressed the thought in his Washington Post column. “They are waging an embarrassingly obvious campaign, hoping he will buckle beneath the pressure of their disapproval and declare Obamacare constitutional,” Mr. Will wrote. Although the court has been famously leakproof, Mr. Will and some of the others are well connected at the court, and I wondered at the time whether they had picked up signals that the chief justice, thought reliable after the oral argument two months earlier, was now wavering, and whether their message was really intended for him.To be sure we know only two new facts for sure and there's nothing in theory improper for a SJC court justice to lobby other justices. However what's new is the idea that they may have leaked to reporters to "encourage" Roberts:
"To be clear, at this point only two facts are confirmed: 1) According to Crawford, Roberts flipped his vote midstream; and 2) someone within the Court must have leaked her this information. It is perfectly appropriate for Justice Kennedy, or any other justice, for that matter, to internally lobby Roberts to try to obtain his vote in an important case. If a member of the Court has turned to conservative columnists like Will or reporters like Crawford in order to pressure and then embarrass Roberts, however, that would be a significant and unusual escalation from the justices’ regular tactics."