TYPO3 Core

Using a flexform like

<numIndex index="2" type="array">
    <numIndex index="0">
        LLL:EXT:rx_shariff/Resources/Private/Language/locallang_be.xlf:flexforms_general.theme.white
    </numIndex>
    <numIndex index="1">white</numIndex>
</numIndex>

will cause the output to contain the label reference instead of the real label.

This is due to the reason that the XML parser passes on the whitespace, hence the output has to be trimmed first before resolving the labels.