There was a great deal of speculation about the conversion from Calvinism to Catholicism of the founder of the Taize community Roger Schutz when he was given Holy Communion at Pope John Paul II Requiem, by the then Cardinal Ratzinger.
According to Cardinal Kaspar he was both!
I just can't see how one can be a Calvinist and Catholic, anymore than one can be an Anglican or a Methodist and a Catholic. I suspect it is one of those strange and ambiguous situations Pope John Paul II loved to create, a sort of personal communion with him.
I am a simple priest, bit thick at times, but I just can't understand this.