I've got a name fairly unfamiliar to many speakers of English, ("Maciej", or "Maciek" in the everyday diminutive form). There aren't any invalid characters in it, but I have on several occasions had it re-written or transcribed by a human being after I've entered it into a form on a website, often to something completely different or garbled (with the implication that I spelled my own name wrong). In particular, my bank did this to me and for about a year and a half I was receiving statements addressed to a "Macie J", where someone had clearly thought the J was part of my middle name (which itself is another tongue twister to English-speaking folks).

No wonder so many immigrants to Canada and the US change their names :)