String StartsWith seems to have trouble with unicode character 712

string ex = "bˈ";
if (ex.StartsWith(ex[0].ToString(), StringComparison.CurrentCulture))
{
     Console.WriteLine("correct");
}
else
{
     Console.WriteLine("wrong");
}

It returns wrong when the second character of the string ex is Unicode character 712
I have tested with a number of other Unicode characters all of which work as expected
Any ideas why this particular Unicode character breaks StartsWith?