Hartington is correct, although at times it is not the legacy system that's the problem but overzealous validation at the web end. Sometimes it is assumed that apostrophes (single quotes) or dashes would never be in a surname, which they unfortunately are (double-barrelled apostrophed surname anyone?)...
There are other idiotic examples of this:
VS for example still requires someone who used to have ILtR in their foreign passport to enter an expiry date for ILtR (ILtR is indefinite, i.e. has no expiry date). When said person changes to British citizenship, an expiry for citizenship is still required. A citizen is a CITIZEN... which means there IS NO EXPIRY DATE! This has been raised with VS in the past, but the question remains whether they'll do anything about it.
S.