I would be interested in reading authoritative interpretations of the filioque which explicitly reject the eternal procession of the Spirit from the Son, and which explicitly state that the only "valid" interpretation of the filioque is in terms of Christ sending the Spirit in the context of creation and our salvation.
I was wrong in one thing. Catholicism does teach that the Holy Ghost proceeds from the Father and the Son both externally (in the economy of salvation) and internally (in the Trinity):
The external relationships of the persons of the Trinity mirror their internal relationships. Just as the Father externally sent the Son into the world in time, the Son internally proceeds from the Father in the Trinity. Just as the Spirit is externally sent into the world by the Son as well as the Father (John 15:26, Acts 2:33), he internally proceeds from both Father and Son in the Trinity. This is why the Spirit is referred to as the Spirit of the Son (Gal. 4:6) and not just the Spirit of the Father (Matt. 10:20).It also teaches that everything the Son has is from the Father, hence both "and from the Son" and "through the Son" mean the same thing.
But you will not see a rejection of the Ghost proceeding from the Son. Both formulas are valid.
Perhaps I should post the Filioque article separately, because this is a theological topic wholly separate from the issue of the appropriatemness and desirability of the Papal visit to Moscow.