@mergen3107: Then that's (probably?) just eInk being eInk

. Older screens can be quirky with specific shades of grays in direct contrast with pure black/white.
I haven't noticed anything out of the ordinary on a H2O or a Forma. But, I can see what you mean on a PW2 (i.e., that the whole width of the bar flashes black first, despite not requesting a flashing update), and I don't think there's anything you can do about it (short of switching to pure B&W and A2 or DU).
(i.e., even -W DU4 -D LEGACY is affected. Only -W DU -D LEGACY will work, because it's B&W. But the Y2 dithering on Kindle is, err, not great, so you probably don't want to use that ;D).
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Yeah, the 1.21.0 release is affected by the issue mentioned, since I fixed it only last night

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That specific usecase turned out to be too roundabout for its own good on Kindle anyway, as the comment explains

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