Duplicate ID in view with iterations and composite components

Question

I have a strange error that only happens sometimes and I can't figure out what is going wrong. I get the following error:

Component ID form_lpm:PODports:PODlocalChargeTable:j_idt1665:j_idt1667:chargeDiv has already been found in the view.

Okay we all know that you can't have duplicate IDs in JSF but that ID above doesn't actually exists! I have something like this:

    <ui:repeat id="PODport">
       <p:dataTable id="PODlocalChargeTable">
            <p:columns>
                <my:compositeComp/>
            </p:columns>
       </p:dataTable>
   </ui:repeat>

The composite component (my:compositeComp) has an ID chargeDiv in there. So in the error message j_idt1665 is the dynamic ID for the p:columns iteration and j_idt1667 the ID for the composite component.

However in the actual generated HTML we get these IDs (as you would expect): The green counter is for the ui:repeat, the blue one for the dataTable and the orange one is for the p:columns.

At first this page is rendered fine (with the IDs shown above) but when I do an ajax request and update the form I get the error with the duplicate ID. The strange thing is that the counters are removed from that ID. Why is that and what can I do?

I have tried to specify IDs for the p:columns (dynCol) and the composite component (compId) and interestingly I now get pretty much the same error but one of the counters is still in the ID:

 <ui:repeat id="PODport">
           <p:dataTable id="PODlocalChargeTable">
                <p:columns id="dynCol">
                    <my:compositeComp id="compId"/>
                </p:columns>
           </p:dataTable>
       </ui:repeat>

Component ID form_lpm:PODports:PODlocalChargeTable:dynCol:2:compId:chargeDiv has already been found in the view

I had the problem with two different composite components. The components were basically just something like this:

<p:outputPanel id="chargeDiv">
    content
</p:outputPanel>
<p:tooltip for="chargeDiv">
    tooltip content
</p:tooltip>

I am using JSF 2.1 (Mojarra 2.1.29-08) and Primefaces 6.1.18

Update: I have done a bit more testing and it is definitely related to the use of composite components. If I have a very simple composite component:

 <cc:implementation>
        <p:outputPanel id="chargeDiv">

        </p:outputPanel>

    </cc:implementation>

and I have dynamic columns like

<p:columns var="myvar" value="#{bean.list}" id="dynCol">
   <my:compositeComp/>
</p:columns>

I get the error with the duplicate ID. If I use the content of the composite component directly in the p:columns:

<p:columns var="myvar" value="#{bean.list}" id="dynCol">
       <p:outputPanel id="chargeDiv">
           content
       </p:outputPanel>  
    </p:columns>

then it works fine.