@rtiangha: The GloHD quirks on specific patterns is a separate issue that's known by Kobo (IIRC, there's even a reply by George about it in this very forum. It might even be referenced in one of the issues in the message you quoted).
(It's tied to specific patterns which require the eInk tech to draw more power to switch. Said behavior depends to some extent on the tech's generation, but it's usually checkered patterns (i.e., specific contrasts over a specific amount of consecutive pixels)).
Dithering patterns are usually full of those, hence the link with dithering
.