We ran into an issue recently where someone was not able to sign up for a paid event because their name did not fit the field parameters. Specifically, their last name has a space in the middle (ie Van Dyke instead of VanDyke). They could not complete the form without removing the space. It was confusing for them to use and me to troubleshoot, but our main concern is that a credit card company could say that the last name does not match the name on their card.
I don't know what the solution would be for this, but when I reached out to support they suggested I submit here :)