Endpoint vs. Group association on Merten devices

[lumbermatt85]

Device : Merten Transmitter 2-Gang Switch (Reference: 506219) (Node 0x06) Device : Merten Receiver Flush-Mounted 2-Gang Switch (Reference: 507502) (Node 0x07) Controler: Z-Wave.Me RaZberry Controller 2016 ZWave+ (Node 0x01) System: Domoticz 2020.2 on Raspberry (OpenZWave Version: 1.6-1033-g3661f170)

I'm trying to get these two Merten devices to work together. The switch (on batteries) has 4 groups corresponding to the 2 pairs of buttons on the switch. They can be seen on the CommandClass 133 (COMMAND_CLASS_ASSOCIATION):

<CommandClass id="133" name="COMMAND_CLASS_ASSOCIATION">
   <Compatibility />
   <State>
      <CCVersion>1</CCVersion>
      <InNif>true</InNif>
      <StaticRequests>4</StaticRequests>
   </State>
<Instance index="1" />
<Associations num_groups="4">
   <Group index="1" max_associations="12" label="Group 1" auto="false" multiInstance="true"/>
   <Group index="2" max_associations="12" label="Group 2" auto="false" multiInstance="true" />
   <Group index="3" max_associations="12" label="Group 3" auto="false" multiInstance="true" />
   <Group index="4" max_associations="12" label="Group 4" auto="false" multiInstance="true" />
</Associations>

The flush mounted switch has two relays which can be switched separately and has to Endpoint as described in the CommandClass 37 (COMMAND_CLASS_SWITCH_BINARY):

<CommandClass id="37" name="COMMAND_CLASS_SWITCH_BINARY">
                <Compatibility />
                <State>
                    <CCVersion>1</CCVersion>
                    <InNif>true</InNif>
                    <StaticRequests>1</StaticRequests>
                </State>
                <Instance index="1" />
                <Instance index="2" endpoint="1" />
                <Instance index="3" endpoint="2" />
                <Value type="bool" genre="user" instance="1" index="0" label="Switch" units="" read_only="false" write_only="false" verify_changes="false" poll_intensity="0" min="0" max="0" value="False">
                    <Help>Turn On/Off Device</Help>
                </Value>
                <Value type="bool" genre="user" instance="2" index="0" label="Switch" units="" read_only="false" write_only="false" verify_changes="false" poll_intensity="0" min="0" max="0" value="False">
                    <Help>Turn On/Off Device</Help>
                </Value>
                <Value type="bool" genre="user" instance="3" index="0" label="Switch" units="" read_only="false" write_only="false" verify_changes="false" poll_intensity="0" min="0" max="0" value="True">
                    <Help>Turn On/Off Device</Help>
                </Value>
            </CommandClass>

The three instances are showing up in Domoticz and I'm able to switch the channels separately. Instance 1 and 2 switches channel A and instance 3 the channel B.

In the OPZW panel in the Function > Group menu, I have following choices for Node 7 : 7, 7.1, 7.2 and 7.3. But when trying to associate e.g. group 1 of the switch with 7.3, OPZW associate the "root" 7 instead of 7.3. Switch works but only operate the first channel A.

I looked at log file, and found following indication in the log OpenZWave_creategroupe.log :

2020-12-05 10:22:52.287 Warning, Node006, MultiChannelAssociation is Present, but MultiChannel CC is not. Trying Plain Association...
2020-12-05 10:22:52.287 Info, Node006, Association::Set - Adding node 7 to group 1 of node 6

Something seems to be wrong at the CC reported by the Flush-Mounted switch. It looks it bit like following issue : #2152 Here enclose a log file with a Refresh Node Info (the XML Config file is empty) for the Flush-Monted switch : OZW_Log.txt And for the switch : OZW_Log_Switch.txt

Thanks for any help with this issue