Why does orbital optimization remove spin contamination? I've come across numerous articles asserting that orbital optimized methods, where minimization of the energy is achieved through a series of unitary rotations (achieved by exponentiated single-electron excitations from the ground state reference) of the reference determinant, are exceptionally good at removing spin contamination. I've seen the numbers they report, and I believe them! I get the gist that orbital optimization allows us to overcome the error introduced by the UHF orbitals, but nowhere can I find the actual explanation of why these rotations effectively cure spin contamination. 

Both references and explanations warmly welcomed.
Upon further thought, I've summarized it as follows. If anyone comes along with a better explanation, they'll get the cake!

Spin contamination is a fictitious effect arising from not achieving the full CI solution to the Schrödinger equation. For, had we found the exact solution, then the solution we found would be an exact eigenfunction of the ${\hat{S}}{}^2$ operator, as $[\hat H, {\hat{S}}{}^2]=0$. 

In a general sense, orbital optimization can be viewed as simply allowing for more correlation to be recovered on top of whatever other improvements you've applied to your initial Hartree-Fock reference. So, by recovering more correlation, you've brought your solution closer to FCI. In doing so, you've brought your solution closer to a solution that contains no spin contamination. 

However, there seems to be a stronger statement that could be made. This type of correlation seems especially potent in removing spin contamination.