Originally posted by mir156 same band here.
Sorry to hear.
I just did the (ISO25600, 30s) test myself: No dark band and no strange white dots.
I have yet to encounter a single issue with any of the three Pentax bodies I have been owning.
I try to not to adapt too early, though. The K-1 made it extremely hard.
Originally posted by MJKoski D810 is better in pulling highlights.
Just a quick remark that technically, such a statement does not make sense.
All sensors have a linear response. There is only one dynamic range, i.e., a single dynamic range figure. Terms like "dynamic range in the shadows" or "dynamic range in the highlights" do not make sense. N.B., I realise you did no use these terms, but you associated "highlight pulling capacity" with a camera model and that does not make sense, unless you are talking about the JPEG engine built into the camera.
How much details is preserved in shadows and highlights depends on the design of tone curves that are used during RAW-"development". One can make these curves transition abruptly (maximising their linear portion) or built in soft "shoulders" that make less of the range linear but give a more "film like" look and lead to a more forgiving exposure experience.
In summary, surely there are differences in how much one can regain (apparently) lost highlights, for instance, but these differences stem from tone curve choices (either in the camera's JPEG engine or in the RAW developer you are using). For years and years, DPReview embarrassed themselves by measuring dynamic range based on JPEGs. They were just measuring tone curve properties, not sensor characteristics. At some point the penny dropped and they stopped the nonsense.
Last comment: To the best of my knowledge the K-1 and the D810 do not share the same chip. You can tell that by the different base ISO values and it will also become apparent once the K-1 has been measured by DxO labs. The D810's chip has slightly more dynamic range. I'm assuming the K-1 uses a variant of the chip used in the D800.