Do you have a pointer to that most recent vote? Everything I can find has solid majorities of both houses voting against closure or transfers, although it is indeed not as solid as I made it out to be in my previous comment.
I'm not sure how much is a change of opinion and how much of it is an erosion of the decision by Democrats to simply deny the issue to Republicans after the Administration fumbled the political optics (or, arguably, was a victim of deliberate, highly-placed sabotage from within on the political optics) to focus on other areas; if you look at the politics of the 2009 vote, it wasn't that both sides were opposed, it was that the Republicans were opposed and doing a full-spectrum attack, and the Democrats collapsed after the administration -- which was pushing to close Guatanamo -- showed incoherence with the testimony of FBI Director Mueller raising concerns of attacks in America if prisoners were transferred to the US. Even simultaneously with the near unanimous votes to block funding for closing Guatanamo, you see many of the Democrats who voted to block funding saying that they supported closing Guatanamo and would vote for it given a specific closure plan that addressed security concerns.
I think the gaps always been there, but a very specific event threw a monkey wrench in the political viability of the Democrats pursuing what was clearly their preference all along.
