A search for "J. Packer" in my Library finds all the books I own by J. I. Packer:

But this does not work in the store:

I used that name just as an example since I own lots of books by him, not that anyone would ever call him "J Packer". But this is an issue for any authors with middle initials. In fact, this might be the general problem which is causing the problem I reported already with author Paul S Fiddes.