rsbessa,
Agreed. Never trust VNAV to avoid the clacker. I also use LVL CHG to regain the path, dip under and then wash off the excess speed before regaining the VNAV path.
Re-setting the new higher speed on the descent page and then re-engaging VNAV is not a good solution in my mind. Firstly, you are no longer descending at the same cost index as before. You may or may not care about that. Secondly, the next time you are kept high you won't have much of a speed margin with which to regain the VNAV path. You have reduced your options.
VNAV is fine for general use provided you input all the winds and temperatures accurately and ATC play your game. With the best will in the world this is a rare occurrence.
