I think we already saw some behavior like this with non-reference design cards. What happened in that case was (presumably): the OEM manufacturer did try to save some costs and did reuse old and adjusted (custom) GPU firmwares with *only-overdrive-5* support for new cards from AMD.
The driver in that case (presumably) did recognize the card itself as a new (the correct) model (which should be overdrive6 of course), but nevertheless overdrive6 did not work (because not working with that firmware?).
If it is the case that you have such a non-reference design AMD GPU, this scenario might be true for you too.
There are very many oclHashcat users which did (or still) use R9 290 or R9 290(x) reference design cards and have no problem with overdrive 6 (and do not get this warning).
This could be a further good argument to always buy reference design cards (besides other factors like better cooling in multi GPU environments etc).
The driver in that case (presumably) did recognize the card itself as a new (the correct) model (which should be overdrive6 of course), but nevertheless overdrive6 did not work (because not working with that firmware?).
If it is the case that you have such a non-reference design AMD GPU, this scenario might be true for you too.
There are very many oclHashcat users which did (or still) use R9 290 or R9 290(x) reference design cards and have no problem with overdrive 6 (and do not get this warning).
This could be a further good argument to always buy reference design cards (besides other factors like better cooling in multi GPU environments etc).