Ken,
I do agree with you.

“ I still thinkif a manufacturer does not recommend something there is a reason.”

That reason in this case is “product liability” When a manufacturer ships loaded ammo he I pretty sure it won’t be altered before it is used and will function as he intended. With the use of components the manufacturer can’t be sure you will do it exactly as the recipe calls out. I believe in the case stated in this post and on other forums the individual did not use the foam fillers correctly. Better to error on the side of caution.
Bill