Vaillant HMU HeatCurve and other config only works after changing definition

[stgm]

For a Vaillant VWL 55/6 with VWZIO but no system thermostat:

Sending the HeatCurve read command does not work (definition from this repo):

r,,,HeatCurve,,,,b51a,05ff348f352d,ign,,IGN:3,,,,ign,,IGN:3,,,,bcd,,BCD,10,,heat curve 0.1 to 4.0
  -->> ERR: invalid position in decode: hmu HeatCurve [b51a05ff348f352d/ff01] 

But removing the 348f does actually make it work:

r,,,HeatCurve,,,,b51a,05FF352D,ign,,IGN:3,,,,bdd,,BCD,10,,heat curve 0.1 to 4.0
  -->> hmu HeatCurve [b51a05ff352d/ff021905000100280001] bdd=[05]0.5 [heat curve 0.1 to 4.0]

I've verified that it's correct by changing the curve on the VWZAI controller and read the status from HMU using ebusd. Questions:

1. What is the meaning of the 348f, assuming that it was put there on purpose some time ago.
2. Why is there a double IGN value in the current definition, is that a mistake?
3. If the current was aimed at a HMU that works differently, Is there a Arotherm specific hmu definition file already?

I am aiming to make it all work so I'd love to submit a PR, but need some context to make sure I'm heading in the right direction.

[stgm]

Seems that the 348f was added in commit 7a4561c which was based on PR #330 by @JongsmaSimon which also contains these bytes in the HeatCurve parameter.
Did that ever work? @wimleers noted that params like HeatCurve did not work for him using PR #330 but that was for a /5 model.

[stgm]

@john30 I think the double IGN:3 may be a mistake originating in the definition of HeatCurve in the tsp that specifies an ignore, but the r_3 that it inherits from does too?

More related to my 348f issues, the tsp has a comment TODO ff34 prefix --- actually, ff seems to be a message id/counter that's repeated in the answer. At least on the VWL /6. I take back the message counter thing a bit. The VWZIO does seem to have a counter-like number there when asking the HMU for this setting, but sending through ebusd it seems that only ff is accepted.