CGEventKeyboardSetUnicodeString（）最多只能处理20个字符

Question

使用非常长的字符串调用此函数：

void postBytes( UniChar *buf, UniCharCount len )
{
    CGEventSourceRef evtSrc = CGEventSourceCreate( kCGEventSourceStatePrivate );
    CGEventRef keyEvtDown = CGEventCreateKeyboardEvent( evtSrc, 0, true );

    CGEventKeyboardSetUnicodeString( keyEventDown, len, buf );
    CGEventPost( kCGHIDEventTap, keyEventDown );

    CFRelease( keyEvtDown );
    CFRelease( evtSrc );
}

无论作为参数提供的字符串如何：当调用CGEventPost()时，只会向事件流发布最多20个字符。此行为未记录。我错过了什么？