That’s definitely a thing too often. The “middlebrow rejection” or something like that. But in this case the OP got a message saying they had exceeded the limit and would get a refund. Then they repeated the transaction at the limit for a total of 20k.
From reading comments here it sounds like the author both misinterpreted things and also compulsively over deposited to test the governments software.
Testing government systems as an outsider is a really bad idea.
Maybe I was primed by the author because I was reading their article, but I understood it the same way they did - the entire $10k was rejected because it put them over the limit. I probably would have tried the same $9975 transaction they did.
Maybe I still don't understand but why didn't he get any I-bonds for either the $10k or the $9975 if they're only refunding the excess? What are you supposed to do if you over-pay? Wait for your refund before buying again?
From reading comments here it sounds like the author both misinterpreted things and also compulsively over deposited to test the governments software.
Testing government systems as an outsider is a really bad idea.