No \mathrel spacing next to ampersands in align environment

Created by: JohnTasto

When using a \mathrel next to an &, the side next to the & loses its extra spacing.

\begin{align}
  x {\mathrel{R}} y  &&  x \mathrel{R} y  &&  x &    \mathrel{R} y  \\
  x {\mathrel{R}} y  &&  x \mathrel{R} y  &&  x & {} \mathrel{R} y  \\
  x {\mathrel{=}} y  &&  x \mathrel{=} y  &&  x &    \mathrel{=} y  \\
  x {         = } y  &&  x          =  y  &&  x &             =  y  \\
\end{align}

The first line is how I believe it should be written, whereas the second line is how I believe it should look, fixed using an empty block. Oddly, when using an = (which is already a relation) inside \mathrel, it has correct spacing, shown in the third line. The fourth line is just a normal relation without \mathrel.

Live example: JS Bin