I know it's a little late to post this, but buying bonds online with AMEX has caused my credit card to be declined three times today.
I bought I Bonds late Tuesday night. The charges showed up on my account Wednesday morning. Today my card was declined for 3 purchases of less than $20, saying I was over my limit. The first two times I called AMEX, the CSR assured me it was an error and my record was noted. The third time I was told it would take 24-48 hours to resolve. Finally I asked for a supervisor, who explained than a hold had been placed for the Bond amount and did not automatically drop off when the charge posted. She then tried to tell me I was very close to my limit. ($6800 under :mad After I told her I was losing SkyMiles, many of them double, she dropped the hold and offereed to give me 1000 miles for my inconvenience. This has never happened to me before, but next time I'll call them first to be sure it doesn't happen again.