Unicode class names in C# - why do some work, when others don't?

I'm wondering why this is. I have two unicode characters from the same group Ll, which is allowed according to the specs: http://msdn.microsoft.com/en-us/library/aa664670%28VS.71%29.aspx

One of them works, the other gives a compile error, and I can't find any documentation on why thi开发者_C百科s is:

This works:

U+0467 CYRILLIC SMALL LETTER LITTLE YUS ѧ

This don't:

U+04FF CYRILLIC SMALL LETTER HA WITH STROKE ӿ

Can you help me find the pattern?

U+0467 is from Unicode 1.1, whereas U+04FF is from Unicode 5.0. The page you refer to mentions Unicode 3.0. So the compiler's Unicode databases are just not new enough.