Hi all,
I have a problem I've not seen until recently.
When I hit save, and throw my own exception: I'm getting a message added to the page: 'Script Thrown Exception'.
This is not a message in the exception that I have made. In addition: it's also adding the desired message from my controller.

Here is what it looks like:



The controller code for the save function is as follows:

//SAVE
public void Save(){
    savepoint sp = Database.setSavePoint();
    try {        
        for(AutoNumber__c r : AutoNumberRecords){
            if(r.Length__c == null || r.Length__c < 1){
                CODException e = new CODException(new MessageCodes.MessageCode('AN900','The Length must be greater than 0'));
                r.Length__c.addError(e);
                throw e;
            }
            if(r.CurrentNumber__c == null || r.CurrentNumber__c < 1){
                CODException e = new CODException(new MessageCodes.MessageCode('AN901','The Length must be greater than 0'));
                r.CurrentNumber__c.addError(e);
                throw e;
            }
        }
        Update AutoNumberRecords;
        NextRecordNames = null;
    } catch (exception e){
        ApexPages.addMessages(e);
        Database.rollback(sp);
    }
}

COD Exception is a custom exception class I've made:

public class CODException extends Exception{

//MESSAGE CODE
private MessageCodes.MessageCode MessageCode{get;set;}

// ADDITIONAL_MESSAGES
//The additional messages stores a list of any information to be appended to an error
//    These could be from DML Exceptions, or multiple errors
private list<string> AdditionalMessages{
    get;
    private set;
}

//COD CODE
//Returns the COD error code
public string GetCode(){
    return  MessageCode != null && MessageCode.Code != null ? MessageCode.Code.toUpperCase() : null;         
}    
    
//COD MESSAGE
//Componse a message from what data we have
private string GetCODMessage(){
    string s = (MessageCode != null && MessageCode.Code != null ? MessageCode.Code : '') + (MessageCode != null && MessageCode.Message != null ? ' - ' + MessageCode.Message: '');
    
    if(AdditionalMessages != null && AdditionalMessages.size() > 0) {   
        for(string am : AdditionalMessages){
            s += '<br/>&bull; ' + am;
        }
    }
    return s;
}

//GET MESSAGE
//The overriden GetMessage method from the standard Exception class
//This is designed to show all the additional information that our exception
//    method has in it. It may be augemented over time
//I am unaware of how the 'escaping' will work when throwing this, or when using a
//    standard sObejct.AddError() method with the escape signature passed in   
public override string GetMessage(){
    return GetCODMessage();
}

//CONSTRUCTORS
//With a MessageCodes.MessageCode and a list of string
public CODException(MessageCodes.MessageCode pMessageCode, string[] pAdditionalMessages) {
    MessageCode = pMessageCode;
    AdditionalMessages = pAdditionalMessages;
}
//With a MessageCodes.MessageCode and a set of string
public CODException(MessageCodes.MessageCode pMessageCode, set<string> pAdditionalMessages) {
    this(pMessageCode, new list<string>(pAdditionalMessages));
}
//With a MessageCodes.MessageCode and a string
public CODException(MessageCodes.MessageCode pMessageCode, string pString) {
    this(pMessageCode,new string[]{pString});
}
//With a MessageCodes.MessageCode
public CODException(MessageCodes.MessageCode pMessageCode) {
    MessageCode = pMessageCode;
}
//With a MessageCodes.Message code and a DML Exception
public CODException(Messagecodes.MessageCode pMessageCode, DMLException pDMLx){
    MessageCode = pMessageCode;
    set<string> s = new set<string>();
    for(integer i = 0; i < pDMLx.getNumDML(); i++){
        s.add(pDMLx.getDmlMessage(i));
    }
    AdditionalMessages = new list<string>(s);
}

}

As well as MessageCodes

public class MessageCodes{
////////// ERROR_AND_MESSAGE_CODES //////////
//A class used to hold all Message codes related to a particular area of the system
//    Populated by a map of code to message, and retrieved as a case insensitive map.Get() type
//    of method. 
//This used to be a listing of enum error codes, but it was discovered that enums will only permit 100 entries
//    so I deprecated that to this

//The class that hold all message codes related to a particular area of the system
public MessageCodes.MessageCode Get(string pCode) {
    MessageCode m;
    if(pCode != null && pCode.DeleteWhiteSpace() != '' && MessageCodeMap.get(pCode.ToUpperCase().trim()) != null) {
        m = new MessageCodes.MessageCode(pCode.ToUpperCase().trim(),MessageCodeMap.get(pCode.ToUpperCase().trim()));
    }
    return m;
}

private map<string,string> MessageCodeMap {
    get {
        if(MessageCodeMap == null) {
            MessageCodeMap = new map<string,string>();
        }
        return MessageCodeMap;
    } private set;
}

//CONSTRUCTOR
//Pass in a map of error code to code message
public MessageCodes(map<string,string> pCodeMessages){
    for(string s : pCodeMessages.KeySet()){
        MessageCodeMap.put(s.ToUpperCase().Trim(),pCodeMessages.get(s));
    }
}

//What is returned after requesting an error message and code
public class MessageCode{
    public string Code {get;private set;}
    public string Message {get;private set;}
    
    public MessageCode(string pCode, string pMessage){
        Code = pCode.ToUpperCase().trim();
        Message = pMessage;
    }
}
}

On top of all that, according to the documentation: if I use the sObject.AddError method it is supposed to prevent any DML from ocurring. (As referenced here: https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_methods_system_sobject.htm#apex_System_SObject_addError) - however it did not.
If I changed the value in one of my fields to forcibly throw the exception: the DML still occurred. So I had to add the Savepoint and rollback to it... Is this right?

Thanks