Never do liberal justices ever vote on the other side.
Simply not true.
Please educate yourself.
Roberts started out as appearing to be conservative. He has been making a gradual shift to liberal though the years. He'd side with the libs on occasion, then come back to the reservation and vote conservative a few times. I think he has now completely made the shift to liberal justice. I think the only time we'll see him vote with the conservatives will be on lopsided decisions like 9-0 or 7-2.
The question is: how long has he been liberal? Did he start out as a conservative and evolve? I think he always was a liberal. His confirmation was Kabuki theater just like Souter's was for Bush 41. I think both Bushes knew they were saddling us with liberal justices.