\phantom is not calculated correctly for =

Hello everyone,


I have found myself resorting to \phantom for some things, and am having
trouble getting it to calculate correctly for the = sign. Would anyone

The following is a piece of Tex code that I copy and pasted from my Lyx
file.

\begin{align*}

\vec{w} & =a+b\\

& \phantom{=}a+b\end{align*}

It should display

w = a+b

a+b

where the second "a+b" should line up perfectly with the first "a+b". This
is not the case.

Thank you

-Patrick