TYPO3 Core

This error occurs when one has a page assigned to a category and tries to export it (and its category record) in XML format via the impexp extension:

There should be a block looking like this example in the export-data, but it is missing:

        <related index="rels" type="array">
            <field index="categories" type="array">
                <type>db</type>
                <relations index="itemArray" type="array">
                    <element index="0" type="array">
                        <id>160</id>
                        <table>sys_category</table>
                    </element>
                </relations>
            </field>
        </related>

As a result, when re-imported, any pages that should be assigned to some category as per the export data, are always additionally assigned to the category with the uid 1 (thus to observe the error on re-import the imported page needs a category with an uid above 1).