Lookup with "Multiple items found" front-end bug?

I have this VF page, with a contact look up field when selected it pre-populate shipping address fields based on contact select. For this example I have two "John Smith" contact records.
If I were to either enter or copy the entire name I get this that pop ups which is expect: before enter to select

When I hit enter this happens: User-added image

The my recent items stay there, I can't click on it nor can I even click on that drop-down menu.
This happens all the time with Firefox, sometimes with Chrome, and never with IE.
Does this ever happens to anyone before? I am using actionRegion in very common way that is pre-populate fields based on look up field selected.

Below is the VF code:

<apex:actionRegion >  
                <apex:pageBlockSection id="Shipto" title="2) Shipment Details" collapsible="false">     
                    <apex:inputField value="{!case.ShipToContact__c}" required="true">
                        <apex:actionSupport event="onchange" action="{!ShipToPopulated}" rerender="Shipto, msgs"/>
                    </apex:inputField>   
                    <apex:outputField value="{!case.Ship_To_Account__c}"/> 
                    <apex:inputField value="{!case.ShippingStreet__c}"/> 
                    <apex:inputField value="{!case.ShippingCity__c}"/> 
                    <apex:inputField value="{!case.ShippingState1__c}"/> 
                    <apex:inputField value="{!case.ShippingPostalCode__c}"/>                                              
                </apex:pageBlockSection>
            </apex:actionRegion>