[NiLuJe]

Ah. Dictionary/popup behavior is indeed left to the mercy of the software implementation, because it's a very fine way to trigger ghosting in a whole lot of different ways (a region of misaligned text right on top of existing text), and flashing when showing the popup and/or when clearing it comes with its own set of potential drawbacks. It's my experience that doing that is better (which is why it's KOReader's default [in fact, the *full* screen is flashed when closing the popup to *really* avoid ghosting]), but I honestly don't recall what Nickel and the Kindle UI do.