A DESCRIPTION OF THE PROBLEM :
https://docs.oracle.com/javase/7/docs/api/java/util/regex/Pattern.html
\p{Lower} A lower-case alphabetic character: [a-z]

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
public class HelloWorld{
     public static void main(String []args){
        Pattern p=Pattern.compile("[\\p{Lower}]",Pattern.CASE_INSENSITIVE);
         
        Matcher m=p.matcher("CF@ampim");
        if(m.find())
                System.out.println(" Result : "+m);
     }
}

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Result : java.util.regex.Matcher[pattern=[a-z] region=0,8 lastmatch=C]
ACTUAL -
 Result : java.util.regex.Matcher[pattern=[\p{Lower}] region=0,8 lastmatch=a]

---------- BEGIN SOURCE ----------
public class HelloWorld{
     public static void main(String []args){
        Pattern p=Pattern.compile("[\\p{Lower}]",Pattern.CASE_INSENSITIVE);
         
        Matcher m=p.matcher("CF@ampim");
        if(m.find())
                System.out.println(" Result : "+m);
     }
}
---------- END SOURCE ----------

CUSTOMER SUBMITTED WORKAROUND :
incase of case-insensitive, use this java regex "[a-z]"

public class HelloWorld{
     public static void main(String []args){
        Pattern p=Pattern.compile("[a-z]",Pattern.CASE_INSENSITIVE);
         
        Matcher m=p.matcher("CF@ampim");
        if(m.find())
                System.out.println(" Result : "+m);
     }
}

FREQUENCY : always