You are right the sample is small, but I had noticed similar patterns in the past - I had also heard the USD conversion stage may give rise to problems.

I would say though that all transactions were on the same date and also booked to my account on the same date regardless of network. I do think that AMEX should avoid this practice as for better or worse its giving them a bad name. I also will not use the card that much outside the Eurozone unless they change their ways.