In the scenario described above (L-forward w/ L-hand blocking down), both directions of rotation are correct - depending on the style of karate/MA you're sensei is teaching.
(1) The clock-wise (or oppositional) rotation was taught to me in a Shotokan dojo. The clockwise rotation facilitated the "wind-up" for a strong Reverse Punch.
(2) The c-clockwise rotation was more of a Shito-ryu technique (of course, not exclusive to Shito-ryu I'm sure). The blocking motion was the launching platform to the Reverse Punch.
Shotokan has been identified w/ larger, more dynamic movements while Shito-ryu is noted for quicker, smaller movements.
This leads me to "Go-no-Sen" vs. "Sen-no-Sen" - the Shotokan example is an example of "Go-no-Sen" while the Shito-ryu example is "Sen-no-Sen". (will be happy to expound if anyone is interested)
Ed Ichihara Smith - Shukokai