I run up against this shit a couple of times a month, because my surname is only a single character. Web forms will routinely insist that I enter my full, legally-recognised surname... even though I already have. It'd be so simple to make these warnings an "are you sure you've entered that right?", like some systems do when you enter an email address with an unusual TLD. But instead I have to lie about my name in order to complete the form (if I'm lucky I get to just append an apostrophe).
And it has knock-on effects. If I'm forced to lie about my name in order to fill in an application for a credit card... the name won't match the name on my file with credit reference agencies and so my credit check will fail (this happened last month, for example).
It can be worked-around: I've learned that when somebody's going to do an identity or credit check that I need to contact them after I lie on their form to ask them to put a human into the process. But it'd be so much simpler if developers trusted that I know what my name is supposed to look like better than they do.