bug#39390: 28.0.50; prettify-symbols-mode confuses display when start/end faces are different

[Raphael 'kena' Poss <knz@thaumogen.net>]

On 16-02-2020 14:34, Eli Zaretskii wrote:

> Actually, I take that back: what's in the buffer is "abc", and it
> displays as a single @.  I simply copy/pasted from your message and
> forgot to delete one @.  Sorry for the confusion.

1) so you agree there's a discrepancy between the configuration (which
should generate a _double_ @) and the display (which displays just one
@). I am expecting the result of the composition to display two @'s. I
would like to understand where this discrepancy comes from.

2) after we settle on what's the expected _display_ you can still see
the display bug as per my further instructions. I am still observing
inconsistent redraws, and I'd like to understand where they come from.

3) My original report was that _regardless of the intended result
display_ (either one or two chars or more), there is a refresh/redisplay
bug when the cursor moves across the composition. Instead of focusing on
the number of characters on the result of composition, I'd like to focus
on the display bug. If you do not observe the display bug with this
particular example config, I can produce a dozen alternate
configurations that demonstrate the bug, with screen recordings of each.
Let me know if that's useful.

Regards,

-- 
Raphael 'kena' Poss