Why does passing an array of Lead objects to an Apex controller action cause an "internal salesforce.com error"?

inputLeadList.cmp

<aura:component controller="ccmt.OneLeadController">
    <aura:attribute name="items" type="Lead[]"/>
    <aura:attribute name="newLead" type="Lead"
                    default="{ 'sobjectType': 'Lead' }"/>
    
    <!-- Event handlers -->
    <aura:handler name="init" value="{!this}" action="{!c.handleInit}"/>
    
    <ui:inputText aura:id="firstName"
                  label="First Name" value="{!v.newLead.FirstName}"
                  required="false"/>
    <ui:inputText aura:id="lastName"
                  label="Last Name" value="{!v.newLead.LastName}"
                  required="true"/>
    <ui:inputText aura:id="company"
                  label="Company Name" value="{!v.newLead.Company}"
                  required="true"/>
    <ui:inputEmail aura:id="email"
                   label="Work Email" value="{!v.newLead.Email}"
                   required="true"/>
	
    <ui:button label="Add Lead" press="{!c.addLead}"/>
    <ui:button label="Submit Lead" press="{!c.save}"/>
</aura:component>

inputLeadListController.js

({
    addLead : function(component, event, helper) {
        var leads = component.get("v.items");
        leads.push(component.get("v.newLead"));
        component.set("v.items", leads);
        
        helper.initNewLead(component);
    },
    handleInit : function(component, event, helper) {
        helper.initNewLead(component);
    },
    save : function(component, event, helper) {
        var self = this;
        
        var createLead = component.get("c.createLead");
        createLead.setParams({
            "newLead": component.get("v.newLead")
        });
        createLead.setCallback(self, function(a) {
            console.log("returned: %o", a.getReturnValue());
        });
        
        $A.enqueueAction(createLead);
    }
})

inputLeadListHelper.js

({
    initNewLead : function(component) {
        var self = this;  // safe reference
        
        var getNewLead = component.get("c.newLead");
        getNewLead.setCallback(self, function(a) {
            console.log("returned: %o", a.getReturnValue());
            component.set("v.newLead", a.getReturnValue());
        });
        
        $A.enqueueAction(getNewLead);
    }
})

oneLead.app

<aura:application controller="ccmt.OneLeadController">
    <aura:attribute name="leads" type="Lead[]"/>
    
	<h1>Lightning-to-Lead</h1>
    
    <ccmt:inputLeadList items="{!v.leads}"/>
    
    <table>
        <thead>
            <tr>
                <th>First Name</th>
                <th>Last Name</th>
                <th>Company</th>
                <th>Email</th>
            </tr>
        </thead>
        <tbody>
            <aura:iteration items="{!v.leads}" var="lead">
                <tr>
                    <td>{!lead.FirstName}</td>
                    <td>{!lead.LastName}</td>
                    <td>{!lead.Company}</td>
                    <td>{!lead.Email}</td>
                </tr>
            </aura:iteration>
        </tbody>
    </table>
    
    <ui:button label="Submit Leads" press="{!c.save}"/>
</aura:application>

OneLeadController.cls

public class OneLeadController {
    
    @AuraEnabled
    public static Id createLead(Lead newLead) {
        insert newLead;
        return newLead.Id;
    }
    
    @AuraEnabled
    public static List<Id> createLeads(List<Lead> newLeads) {
        insert newLeads;
        
        List<Id> newLeadIds = new List<Id>();
        for (Lead eachLead : newLeads) {
            newLeadIds.add(eachLead.Id);
        }
        
        return newLeadIds;
    }
    
    @AuraEnabled
    public static Lead newLead() {
        return (Lead)Lead.sObjectType.newSObject(null, true);
    }
}

oneLeadController.js

({
    save : function(component, event, helper) {
        var self = this;
        
        var createLeads = component.get("c.createLeads");
        createLeads.setParams({
            "newLeads": component.get("v.leads")
        });
        createLeads.setCallback(self, function(a) {
            console.log("returned: %o", a.getReturnValue());
        })
        
        $A.enqueueAction(createLeads);
    }
})

I am seeing one gap inputLeadListController.js..file. while clicking on first Save button record was not creating. and then I did some small changes in it. and its working perfectly.

Now this js look like this.

({
addLead : function(component, event, helper) {
var leads = component.get("v.items");
leads.push(component.get("v.newLead"));
component.set("v.items", leads);

    helper.initNewLead(component);
},
handleInit : function(component, event, helper) {
    helper.initNewLead(component);
},
save : function(component, event, helper) {
     var self = this;
     var led=component.get("v.newLead");
     led.sobjectType='Lead';

    var createLead = component.get("c.createLead");
    createLead.setParams({"newLead": led});
    createLead.setCallback(self, function(a) {
        console.log("returned: %o", a.getReturnValue());
    });

    $A.enqueueAction(createLead);
}

})

I added this sobjectType

var led=component.get("v.newLead");
led.sobjectType='Lead';
..