In my game I've faced 2 1861 attacks on Richmond. The first was defended by a Corps led by Hugar. Also involved in the battle window was Lee. Despite being attacked (or supporting the defense, dunno) he didn't activate. Still had the padlock.
A month later (Jan, 1862), Richmond was again attacked. This time Lee was the only stack there and defended well. Again, he did not activated.
Any explanation will do, thx!