Word, Excel and PowerPoint 2016 (16.0.6366.2036) the images and the callback for the backstage view are no longer working

Question

In the latest build of Word, Excel and PowerPoint 2016 (16.0.6366.2036) (desktop version) the images defined in the CustomUI for the backstage view are no longer shown. In the following config file, the HappyFace or any specified image per se won't be shown by the application.

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui" onLoad="OnRibbonLoaded" loadImage="getImages">
    <backstage>
        <tab idMso="TabRecent">
            <firstColumn>
                <taskFormGroup idMso="GroupOpenPlaces">
                    <category idMso="ButtonCategoryRecentDocuments">
                        <task id="task1" label="My main task" insertAfterMso="ButtonTaskRecentDocuments" imageMso="HappyFace">
                        </task>
                    </category>
                </taskFormGroup>
            </firstColumn>
        </tab>
    </backstage>
</customUI>

Also the callback e.g. getLabel and getHelperText, etc. defined for the group within the backstage view are not getting called. See the example below. The callback "getGroupLabel" and "getGroupHelperText" are not being called.

<customUI xmlns="http://schemas.microsoft.com/office/2009/07/customui" onLoad="OnRibbonLoaded" loadImage="getImages">
    <backstage>
        <tab idMso="TabInfo">
            <firstColumn>
                <group id="group1" getLabel="getGroupLabel" getHelperText="getGroupHelperText" insertBeforeMso="GroupPermissions">
                </group>
            </firstColumn>
        </tab>
    </backstage>
</customUI>

These were working in the earlier build of Office 2016. Please advise if there is a workaround, and if this is by design. Thanks.