JSON filter with HTML subfilter creates duplicated TU ids

The following JSON file, processed with the default settings + okf_html set for the sub-filter produces an XLIFF file where the two trans-units have the same ID.

JSON:

{ 
    BACK_TO_CHECKOUT: 'Back to checkout',
    CHECKOUT: 'Checkout'
}

XLIFF:

<group id="sg1">
    <group id="sg1_ssf1" resname="sub-filter:BACK_TO_CHECKOUT">
        <trans-unit id="sg1_tu1" resname="BACK_TO_CHECKOUT_1">
            <source xml:lang="en-us">Back to checkout</source>
            <target xml:lang="fr-fr">Back to checkout</target>
        </trans-unit>
    </group>
    <group id="sg1_ssf2" resname="sub-filter:CHECKOUT">
        <trans-unit id="sg1_tu1" resname="CHECKOUT_1">
            <source xml:lang="en-us">Checkout</source>
            <target xml:lang="fr-fr">Checkout</target>
        </trans-unit>
    </group>
</group>

Both TU have sg1_tu1 as the id.