Nokia N78 Retrieved wrong mobile grading

i use like this:
$detect = new Mobile_Detect;
$detect->setUserAgent("NOKIAN78/UCWEB 8.6.0.180/28/999");
$grade = $detect->mobileGrade();
the grade turned to be "B",which was expected to be "C".
I found the following statments always returned true
"$this->version('iPad', self::VERSION_TYPE_FLOAT)<4.3" 
so i changed it to  "$this->isIOS() && $this->version('iPad', self::VERSION_TYPE_FLOAT)<4.3"