Having two identical last names is very common in Spain, for purely combinatorial/statistical reasons. No one bats an eye about that. It would only suggest inbreeding if they were extremely uncommon last names.
I bet she just made a face because the second surname is part of people's identity and has a meaning, it's not something people would fake. And it's also used when e.g. checking your ID to see that you are the legitimate owner of the account, so it probably wouldn't even work.
Of course it's totally reasonable that you suggested that in that case, what's unreasonable is the bank's system requirement of two last names, but to an average Spanish person it sounds odd to want to use a second surname that isn't real.
I know a person who has some certificates to the name of Firstname Lastname NULL :)
I bet she just made a face because the second surname is part of people's identity and has a meaning, it's not something people would fake. And it's also used when e.g. checking your ID to see that you are the legitimate owner of the account, so it probably wouldn't even work.
Of course it's totally reasonable that you suggested that in that case, what's unreasonable is the bank's system requirement of two last names, but to an average Spanish person it sounds odd to want to use a second surname that isn't real.
I know a person who has some certificates to the name of Firstname Lastname NULL :)